Polymer foam articles and methods of making polymer foams

ABSTRACT

Molded polymer foam articles are described as having a novel a foam structure. The polymer foam articles include a continuous polymer matrix defining a plurality of pneumatoceles therein which is present throughout the entirety of the article, including in the surface region extending 500 microns beneath the surface of the article. The surface region is further characterized as having compressed pneumatoceles. The novel foam structure is achieved even when molding polymer foam articles comprising a thickness of more than 2 cm, a volume of more than 1000 cm 3 ; or both a volume of more than 1000 cm 3  and a thickness of more than 2 cm. Methods of making the molded polymer foam articles are also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/077,686, filed Oct. 22, 2020, entitled “POLYMER FOAM ARTICLES ANDMETHODS OF MAKING POLYMER FOAMS,” which is a continuation of U.S. patentapplication Ser. No. 16/914,993, filed Jun. 29, 2020, entitled “POLYMERFOAM ARTICLES AND METHODS OF MAKING POLYMER FOAMS,” which claims thebenefit of U.S. Provisional Application No. 62/867,516, entitled “METHODFOR MOLTEN FOAM INJECTION MOLDING OF FOAMED PARTS”, filed Jun. 27, 2019,the contents of all of which are hereby incorporated in their entiretyby reference.

BACKGROUND

Foamed polymer articles are widely employed in the industry due to thehighly desirable attribute of providing high strength associate withsolid polymer articles, while also delivering a reduction of density andtherefore in the amount of polymer used to form an article of a selectedvolume. Additionally, the industry enjoys the benefits provided by thereduction in the weight of a foamed article compared with its solidcounterpart, while still obtaining the benefits of strength, toughness,impact resistance, etc. delivered by the polymer itself.

The industry has thus developed several now-conventional methods toentrain gas into thermoplastic polymers to make such foam articles. Tomold a foamed thermoplastic polymer article using a gas, commercialguidelines and industrial practice employ a melt mixing apparatusoperable to maintain a pressure to limit expansion of a gas in theinterior of the apparatus while melt mixing the gas or a source of a gaswith the thermoplastic polymer, further at a temperature above a melttemperature of the thermoplastic polymer. Such processes and apparatusesare designed to minimize formation of pneumatoceles, or pockets of gas,that would otherwise form by expansion of the gas in the moltenthermoplastic polymer. Thus, while residing within and disposed withinthe melt mixing apparatus, a thermoplastic polymer may include a sourceof a gas or the gas itself dissolved or dispersed therein, whileincluding no pneumatoceles or substantially no pneumatoceles. A mixtureof molten thermoplastic polymer and a gas that is at or above thetemperature at which it would form pneumatoceles at atmosphericpressure, while including no pneumatoceles or substantially nopneumatoceles may be referred to as a molten pneumatic mixture. Thetemperature at which the gas, or pneumatogen, would form pneumatocelesin the molten pneumatic mixture at atmospheric pressure may be referredto as the critical temperature. Melt mixing apparatuses well known inthe art are thus designed and adapted to make and dispense moltenpneumatic mixtures. Further, such apparatuses are suitable to makemolten pneumatic mixtures by adding a nascent, latent, or potential gasthat is released at a characteristic temperature or that forms byexothermic or endothermic chemical reaction at a characteristictemperature. The critical temperature of a nascent, latent, or potentialgas is the temperature at which the reaction occurs or a gas is releasedinto the thermoplastic polymer. All such materials and processes arewell understood and melt mixing apparatuses of varying design are widelyavailable commercially for this purpose. Melt mixing apparatusescommonly employed are single screw or twin screws extruders modified tohave a pressurized chamber at the distal end of the screw to receive aset amount, or “shot” of a molten pneumatic mixture that travels duringmixing by operation of the screw to urge the molten pneumatic mixturetoward the pressurized chamber.

Upon building up the set amount or shot in the pressurized chamber, themolten pneumatic mixture is dispensed from the melt mixing apparatus andis directed by fluidly connected tubes, pipes, etc. into the cavity of amold that obtains a desired shape. Dispensing is generally carried outto maximize the amount of foaming (pneumatocele formation) that occursin the mold cavity by release of the pressure while the thermoplasticpolymer is still molten. The expanded foam in the cavity is then cooledto result in a foamed article. Foamed parts molded using thismethodology are referred to in the art as injection molded foam parts.The techniques are generally limited in scope to make parts havingthicknesses of about 2 cm or less.

Injection molding processes employing pneumatogen sources to induce afoam structure in molded parts can be understood from a recentpeer-reviewed journal article by Bociaga et al., “The influence offoaming agent addition, talc filler content, and injection velocity onselected properties, surface state, and structure of polypropyleneinjection molded parts.” Cellular Polymers 2020, 39(1) 3-30. In thispublication the process conditions typically employed for molding ofstandard injection molded ISO test bars of 4.1 mm thickness weresystematically changed to create 16 different combinations of theprocess settings and formulation variables (concentration of pneumatogensource, filler content, injection velocity, injection time, hold time,and hold pressure). The authors teach that manipulating the process andformulation produces some changes in the foam structure in the resultingfoam parts, but all the variables produced parts having a “skin layer”,which is a term of art to describe a highly characteristic region nearthe surface of an injection molded foam article that is free orsubstantially free of pneumatoceles.

Inspection of the surface of an injection molded foamed article, and ofthe area extending about 500 microns beneath the surface in anydirection, reveals a solid thermoplastic region—that is, the regions isfree of pneumatoceles or substantially free of pneumatoceles. Foam partsarising from injection molding in accordance with conventional injectionmolding processes include the skin layer feature. Additionally, the skinlayer of most such parts is significantly thicker than 500 μm and may be1 mm, 2 mm, 3 mm, or even thicker depending on the methods, apparatuses,and materials employed.

In order to make large foamed parts (such as pallets or wheelbarrowbodies, for example), the conventional processes above are insufficientbecause the large mold cavities induce an excess pressure drop as themolten pneumatic mixture flows and expands during filling of the mold,and the pneumatoceles may form but then coalesce or leak from theviscous polymer flow during filling. Thus, in some cases of “structuralfoam” molding, multiple nozzles are used simultaneously to fill large orthick mold cavities quickly. In other cases significant backpressure maybe applied within the mold cavity to prevent pneumatocele formationduring filling; release of pressure after filling the mold operates toallow pneumatocele formation substantially within the mold cavity. Bothapproaches are often used in a single process.

However, the foregoing structural foam molding processes do not solve aproblem that has effectively blocked the industry from developing verylarge parts. As is well understood, areas near the surface of a moltenmass will cool more rapidly than the interior thereof, and a coolinggradient of temperature develops within the mass. The cooling rate atpoints deepest within the mass are the slowest. In terms of large moldcavities filled with a mass of molten polymer or pneumatic mixture, aninterior region of the mass may cool so slowly that viscous flow of thethermoplastic allows pneumatocele coalescence, forming largepolymer-free pockets and disrupting the intended continuous polymermatrix defining such foams. This effect may be exacerbated by shrinkageof polymer volume as it cools to a temperature below a melt transitionthereof. For large foamed parts, this effect can even lead to completecollapse of the foam structure in the interior of the part.

The combined strength and density reduction associated with foamedarticles is not realized without a continuous polymer matrix throughoutthe part. Foamed parts having large polymer-free areas or voidscompromise the structural integrity of the part, which makes such partsunfit for its intended use. These severe technical issues have limitedthe industrial application of polymer foams to many otherwise highlyuseful and beneficial applications. Accordingly, there is an ongoingneed to provide improved methods for making foamed articles,particularly large or thick foamed articles. There is an ongoing need toobtain parts having a continuous foam structure throughout. There is aparticular need to obtain parts having a thickness greater than 2 cm andhaving a continuous foam structure throughout. There is an ongoing needin the industry to address such needs using conventional apparatuses andmaterials.

SUMMARY OF THE INVENTION

Described herein is a method of making a molten polymer foam. The methodincludes: adding a thermoplastic polymer and a pneumatogen source to anextruder; heating and mixing the thermoplastic polymer and pneumatogensource in the extruder under a pressure to form a molten pneumaticmixture, wherein the temperature of the molten pneumatic mixture exceedsthe critical temperature of the pneumatogen source; collecting an amountof the molten pneumatic mixture in a collection region of the extruder;defining an expansion volume in the collection region to cause apressure to drop in the collection region; allowing an expansion periodof time to elapse after the defining; and dispensing a molten polymerfoam from the collection region. In embodiments, the expansion volume isselected to provide between 10% and 300% of the total expected moltenfoam volume in the collection area. In embodiments, the expansion periodis between 5 seconds and 600 seconds. In embodiments, the moltenpneumatic mixture is undisturbed or substantially undisturbed during theexpansion period.

In embodiments the dispensing is dispensing to a forming element; insome embodiments the forming element is a mold. In embodiments there isa fluid connection between the collection region of the extruder and themold. In embodiments, the dispensing is an unimpeded flow of the moltenpolymer foam. In embodiments, the dispensing is a linear flow of moltenpolymer foam.

In embodiments the method further comprises cooling the dispensed moltenpolymer foam to a temperature below a melt transition of thethermoplastic polymer. In embodiments, one or more additional materialsto the extruder, wherein the one or more materials are selected fromcolorants, stabilizers, brighteners, nucleating agents, fibers,particulates, and fillers. In embodiments the pneumatogen source is apneumatogen and the addition is a pressurized addition. In otherembodiments the pneumatogen source comprises a bicarbonate, apolycarboxylic acid or a salt or ester thereof, or a mixture thereof.

Also disclosed herein is a polymer foam article made in using themethods, materials, and apparatuses described herein. In embodiments,the polymer foam article has a foam structure throughout the entiretythereof characterized as a continuous polymer matrix defining aplurality of pneumatoceles therein. In embodiments, a surface region ofa polymer foam article comprises compressed pneumatoceles. Inembodiments, the surface region is the region extending 500 microns fromthe surface of the article.

Also disclosed herein are thermoplastic polymer foam articles, thearticle having a foam structure throughout the entirety thereof that isa continuous polymer matrix defining a plurality of pneumatocelestherein, further wherein a surface region of the article comprisescompressed pneumatoceles. In some embodiments, the surface region is theregion of the article extending 500 microns from the surface thereof. Insome embodiments, the article comprises compressed pneumatoceles morethan 500 microns from the surface thereof. In embodiments, the polymerfoam article comprises a thickness of more than 2 cm; in otherembodiments the polymer foam article comprises a volume of more than1000 cm³, 1000 cm³ to 5000 cm³, or even more than 5000 cm³; and in stillother embodiments, the polymer foam article comprises a volume of morethan 1000 cm³ and a thickness of more than 2 cm, a volume between 1000cm³ and 5000 cm³ and a thickness of more than 2 cm, or a volume of morethan 5000 cm³ and a thickness of more than 2 cm.

In embodiments, materials used to make the polymer foam articles are notparticularly limited and include thermoplastic polymers selected frompolyolefins, polyamides, polyimides, polyesters, polycarbonates, poly(lactic acid)s, acrylonitrile-butadiene-styrene copolymers,polystyrenes, polyurethanes, polyvinyl chlorides, copolymers oftetrafluoroethylene, polyethersulfones, polyacetals, polyaramids,polyphenylene oxides, polybutylenes, polybutadienes, polyacrylates andmethacryates, ionomeric polymers, poly ether-amide block copolymers,polyaryletherkeytones, polysulfones, polyphenylene sulfides,polyamide-imide copolymers, poly(butylene succinate)s, cellulosics,polysaccharides, and copolymers, alloys, admixtures, and blends thereof.In some embodiments, the thermoplastic polymer is a mixed plastic wastestream. The continuous polymer matrix optionally further includes one ormore additional materials selected from colorants, stabilizers,brighteners, nucleating agents, fibers, particulates, and fillers.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1B illustrate a melt mixing apparatus useful for carrying outthe methods described herein.

FIG. 2-1 is a photographic image of a part molded according to thestandard foam molding process as described in Example 1.

FIG. 2-2 is a photographic image of a part molded according to amolten-foam injection molding (MFIM) process as described in Example 1.

FIG. 2-3 is a photographic image of a piece cut from the part madeaccording to the standard foam molding process as described in Example1.

FIG. 2-4 is a photographic image of a piece cut from the part madeaccording to the MFIM process as described in Example 1.

FIG. 2-5 is a photographic image of a piece cut from the part madeaccording to the standard foam molding process as described in Example1.

FIG. 2-6 is a photographic image of a piece cut from the part madeaccording to the MFIM process as described in Example 1.

FIG. 3A is a photographic image of a cross section of Part A madeaccording to a standard foam molding process and cut into two pieces toreveal a cross section, as described in Example 2.

FIG. 3B is a photographic image of a cross section of Part B madeaccording to an MFIM process and cut into two pieces to reveal a crosssection, as described in Example 2.

FIG. 4A is a photographic image of a cross section of Part C madeaccording to an MFIM process and cut into two pieces to reveal a crosssection, as described in Example 2.

FIG. 4B is a photographic image of a cross section of Part D madeaccording to a standard foam molding process and cut into two pieces toreveal a cross section, as described in Example 2.

FIG. 5 is a graph including plots of part density versus decompressionvolume for various decompression times for Trial B as described inExample 3.

FIG. 6 is a graph including plots of strain versus time for parts madein Trials A, B, and C as described in Example 4.

FIG. 7 shows photographic images of views in different aspects of PartsA, B, and C as described in Example 4.

FIG. 8 shows photographic images views of cross sections of Part A′, B′,C′, and D′ as described in Example 4.

FIG. 9 is a drawing of two parts as described in Example 5.

FIG. 10 is an isometric image of a tomography scan of the first partmade according to an MFIM process as described in Example 6.

FIG. 11 is an image of the cross section plane shown in FIG. 10 asdescribed in Example 6.

FIG. 12 is a graph including plots of average cell size and cell countagainst cell circularity for the first part made as described in Example6.

FIG. 13 is drawing of an X-ray tomographic image of a cross section of asecond (spherical) part as described in Example 6.

FIG. 14 is a graph including plots of average cell size and cell countagainst cell circularity for the second (spherical) part made asdescribed in Example 6.

FIG. 15 is a micrograph of a fracture surface of a fractured three-inchdiameter composite sphere made according to an MFIM process, asdescribed in Example 7.

FIG. 16 is an image a micrograph of a fracture surface of a fracturedthree-inch diameter composite sphere made according to an MFIM process,as described in Example 7.

FIG. 17 is an image a micrograph of a fracture surface of a fracturedthree-inch diameter composite sphere made according to an MFIM process,as described in Example 7.

FIG. 18 is an image a micrograph of a fracture surface of a fracturedthree-inch diameter composite sphere made according to an MFIM process,as described in Example 7.

FIG. 19 shows micrograph images of cross sections from ISO bar partsmade according to standard foam molding process runs 10, 11, 14, and 15,as described in Example 8.

FIG. 20 shows micrograph images of cross sections from ISO bar partsmade according to MFIM process runs 9, 10, 15, and 16, as described inExample 8.

FIG. 21 shows a micrograph of a cross section of an ISO bar part madeaccording to the MFIM process of Run 9 and stress-strain plots ofreplicate parts made according to the MFIM process of Run 9, asdescribed in Example 8.

FIG. 22 includes a micrograph of a cross section of an ISO bar part madeaccording to the standard foam molding process of Run 10 andstress-strain plots of replicate parts made according to the standardfoam molding process of Run 10, as described in Example 8.

FIG. 23 includes two images from X-ray tomography of an ISO bar partmade according to the standard foam molding process of Run 15, asdescribed in Example 8.

FIG. 24 includes two images from X-ray tomography of an ISO bar partmade according to the MFIM process of Run 9, as described in Example 8.

FIG. 25 is an image from an X-ray scan of a large tensile bar part madeaccording to an MFIM process, as described in Example 9.

FIG. 26 includes cross sections of eight large tensile bar parts madeaccording to MFIM processes, as described in Example 9.

FIG. 27 is an X-ray tomography image of a large tensile bar part madeaccording to an MFIM process, as described in Example 9.

FIG. 28 includes a series of X-ray tomographic images at differentdepths within a tensile bar part made according to an MFIM process and aseries of images at different depths within a tensile bar part madeaccording to a standard foam molding process, as described in Example10.

FIG. 29 is a graph including a plot of cell count versus depth for thetensile bar part made according to an MFIM process and a plot of cellcount versus depth for the tensile bar part made according to a standardfoam molding process, as described in Example 10.

FIG. 30 is a graph including a plot of cell circularity versus depth forthe tensile bar part made according to an MFIM process and a plot ofcell circularity versus depth for the tensile bar part made according toa standard foam molding process, as described in Example 10.

FIG. 31 is a graph including a plot of cell size versus depth for thetensile bar part made according to an MFIM process and a plot of cellsize versus depth for the tensile bar part made according to a standardfoam molding process, as described in Example 10.

FIG. 32 is a photograph of Sample 20 made according to a reverse MFIMprocess, as described in Example 12.

FIG. 33 is a photograph of Sample 10 made according to an MFIM process,as described in Example 12.

FIG. 34 is a photograph showing a cross section of Sample 20 madeaccording to a reverse MFIM process, as described in Example 12.

FIG. 35 is a photograph showing a cross section of Sample 10 madeaccording to an MFIM process, as described in Example 12.

FIG. 36 is a plot of cell count versus depth (distance from surface) forSample 10 (MFIM) and Sample 20 (Reverse MFIM) as described in Example12.

FIG. 37 is a plot of cell size versus depth (distance from surface) forSample 10 (MFIM) and Sample 20 (Reverse MFIM) as described in Example12.

FIG. 38 is a graph including a plot of averaged stress versus strain forSample 10 (MFIM) and a plot for Sample 20 (Reverse MFIM) fromcompression modulus measurements, as described in Example 12.

FIG. 39 is a graph including a plot of averaged stress versus strain forSample 10 (MFIM) and a plot for Sample 20 (Reverse MFIM) from flexuralmodulus measurements, as described in Example 12.

FIG. 40 is a graph of plots of stress versus strain from compressionmodulus measurements made of three metallocene polyethylene (mPE)materials of different densities and made according to MFIM processes,as described in Example 14.

FIG. 41 illustrates a mold configuration useful for carrying out themethods described herein.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Although the present disclosure provides references to preferredembodiments, persons skilled in the art will recognize that changes maybe made in form and detail without departing from the spirit and scopeof the invention. Various embodiments will be described in detail withreference to the drawings, wherein like reference numerals representlike parts and assemblies throughout the several views. Reference tovarious embodiments does not limit the scope of the claims attachedhereto. Additionally, any examples set forth in this specification arenot intended to be limiting and merely set forth some of the manypossible embodiments for the appended claims.

Unless otherwise defined, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art. In case of conflict, the present document, includingdefinitions, will control. Preferred methods and materials are describedbelow, although methods and materials similar or equivalent to thosedescribed herein can be used in practice or testing of the presentinvention. All publications, patent applications, patents and otherreferences mentioned herein are incorporated by reference in theirentirety. The materials, methods, and examples disclosed herein areillustrative only and not intended to be limiting.

As used herein, “polymer matrix”, including “continuous polymer matrix”,“thermoplastic polymer matrix”, “molten polymer matrix” and like termsrefer to a continuous solid or molten thermoplastic polymer phase or anamount of a solid or molten thermoplastic polymer defining a continuousphase.

As used herein, “molten mixture” means a molten thermoplastic polymer ormixture of molten thermoplastic polymers, optionally including one ormore additional materials mixed with the molten thermoplastic polymer ormixture thereof.

As used herein, “molten pneumatic mixture” means a mixture of athermoplastic polymer and a pneumatogen source, wherein the polymer isat a temperature above a melt temperature thereof and the temperature ofthe mixture exceeds the critical temperature of the pneumatogen source,further wherein the mixture is characterized as having no pneumatocelesor substantially no pneumatoceles. The molten pneumatic mixture ispresent under a pressure sufficient to prevent pneumatocele formation,or substantially prevent pneumatocele formation, or cause thepneumatogen source to be dissolved or dispersed within the thermoplasticpolymer either as a gas or a supercritical liquid. “Substantiallyprevent pneumatocele formation”, “substantially no pneumatoceles” andlike terms with respect to a molten pneumatic mixture means that whilepressure conditions may be used to prevent pneumatocele formation in amolten mixture, defects, wearing of parts, and the like in processingequipment may cause unintentional pressure loss that does not interfereoverall with obtaining and maintaining a pressurized molten mixture.

As used herein, “foam”, “polymer foam”, thermoplastic polymer foam”,“molten foam”, “molten polymer foam” and similar terms refer generallyto a continuous polymer matrix defining a plurality of pneumatoceles asa discontinuous phase dispersed therein.

As used herein, the term “pneumatocele” means a discrete void defined byand surrounded by a continuous thermoplastic polymer matrix.

As used herein, the term “pneumatogen” means a gaseous compound capableof defining a pneumatocele within a molten thermoplastic polymer matrix.

As used herein, the term “critical temperature” means the temperature atwhich a pneumatogen source produces a pneumatogen at atmosphericpressure.

As used herein, the term “pneumatogen source” refers to a latent,potential, or nascent pneumatogen, added to or present within athermoplastic polymer matrix, such as dissolved in the matrix and/orpresent as a supercritical fluid therein; or in the form of an organiccompound that produces a pneumatogen by a chemical reaction; or acombination of these; or wherein the pneumatogen source is apneumatogen, becomes a pneumatogen, or produces a pneumatogen at acritical temperature characteristic of the pneumatogen source.

The terms “comprise(s),” “include(s),” “having,” “has,” “can,”“contain(s),” and variants thereof, as used herein, are intended to beopen-ended transitional phrases, terms, or words that do not precludethe possibility of additional acts or structures. The singular forms“a,” “and” and “the” include plural references unless the contextclearly dictates otherwise. The present disclosure also contemplatesother embodiments “comprising,” “consisting of’ and “consistingessentially of,” the embodiments or elements presented herein, whetherexplicitly set forth or not.

As used herein, the term “optional” or “optionally” means that thesubsequently described event or circumstance may but need not occur, andthat the description includes instances where the event or circumstanceoccurs and instances in which it does not.

As used herein, the term “about” modifying, for example, the quantity ofan ingredient in a composition, concentration, volume, processtemperature, process time, yield, flow rate, pressure, and like values,and ranges thereof, employed in describing the embodiments of thedisclosure, refers to variation in the numerical quantity that canoccur, for example, through typical measuring and handling proceduresused for making compounds, compositions, concentrates or useformulations; through inadvertent error in these procedures; throughdifferences in the manufacture, source, or purity of starting materialsor ingredients used to carry out the methods, and like proximateconsiderations. The term “about” also encompasses amounts that differdue to aging of a formulation with a particular initial concentration ormixture, and amounts that differ due to mixing or processing aformulation with a particular initial concentration or mixture. Wheremodified by the term “about” the claims appended hereto includeequivalents to these quantities. Further, where “about” is employed todescribe a range of values, for example “about 1 to 5” the recitationmeans “1 to 5” and “about 1 to about 5” and “1 to about 5” and “about 1to 5” unless specifically limited by context.

As used herein, the term “substantially” means “consisting essentiallyof”, as that term is construed in U.S. patent law, and includes“consisting of” as that term is construed in U.S. patent law. Forexample, a composition that is “substantially free” of a specifiedcompound or material may be free of that compound or material, or mayhave a minor amount of that compound or material present, such asthrough unintended contamination, side reactions, or incompletepurification. A “minor amount” may be a trace, an unmeasurable amount,an amount that does not interfere with a value or property, or someother amount as provided in context. A composition that has“substantially only” a provided list of components may consist of onlythose components, or have a trace amount of some other componentpresent, or have one or more additional components that do notmaterially affect the properties of the composition. Additionally,“substantially” modifying, for example, the type or quantity of aningredient in a composition, a property, a measurable quantity, amethod, a value, or a range, employed in describing the embodiments ofthe disclosure, refers to a variation that does not affect the overallrecited composition, property, quantity, method, value, or range thereofin a manner that negates an intended composition, property, quantity,method, value, or range. Where modified by the term “substantially” theclaims appended hereto include equivalents according to this definition.

As used herein, any recited ranges of values contemplate all valueswithin the range and are to be construed as support for claims recitingany sub-ranges having endpoints which are real number values within therecited range. By way of a hypothetical illustrative example, adisclosure in this specification of a range of from 1 to 5 shall beconsidered to support claims to any of the following ranges: 1-5; 1-4;1-3; 1-2; 2-5; 2-4; 2-3; 3-5; 3-4; and 4-5.

In embodiments disclosed herein, a method of extruding a molten polymerfoam comprises, consists essentially of, or consists of adding athermoplastic polymer and a pneumatogen source to an inlet situated on afirst end of an extruder; heating and mixing the thermoplastic polymerand the pneumatogen source in the extruder to form a molten pneumaticmixture, wherein the temperature of the molten pneumatic mixture exceedsthe critical temperature of the pneumatogen source; collecting an amountof the molten pneumatic mixture in a barrel region of the extruderlocated proximal to a second end of the extruder; forming an expansionvolume in the barrel region, wherein the forming causes a pressure todrop in the barrel region; allowing a period of time to elapse after thepressure drop; and dispensing a molten polymer foam from the extruder.

In embodiments, the extruder is any machine designed and adapted formelting, mixing, and dispensing thermoplastic polymers and mixturesthereof, optionally with one or more additional materials such asfillers, nucleating agents, diluents, stabilizers, brighteners, and thelike; and further wherein the extruder includes a collection area for acollecting a mass of mixed, molten material and further is capable offorming an expansion volume in the collection area that is coupled witha pressure drop. Extruders are well known in the industry and arebroadly used for melting, mixing, and manipulating molten thermoplasticpolymers. In embodiments, the extruder is adapted and designed formelting, mixing, and dispensing a mixture of a thermoplastic polymer anda pneumatogen source. Such extruders are adapted to obtain moltenpneumatic mixtures under a pressure sufficient to prevent orsubstantially prevent pneumatocele formation in the molten pneumaticmixture.

In embodiments, extruders useful to carry out the present methodsinclude an interior volume, referred to in the art as the “barrel” ofthe extruder, designed and adapted for receiving a solid thermoplasticpolymer, further for carrying out the melting and mixing thereof. Inembodiments, the extruder defines an interior volume designed forreceiving a solid thermoplastic polymer and a pneumatogen or apneumatogen source, further for carrying out the melting of at least thepolymer and for mixing the pneumatogen or pneumatogen source with themolten polymer to obtain a molten pneumatic mixture. In embodiments theextruder further includes a collection area for a collecting a mass of amolten pneumatic mixture material. In embodiments the extruder furtherincludes means of forming an expansion volume in the collection areathat is coupled with a pressure drop.

In embodiments, the extruder is an injection molding machine. Inembodiments, the extruder is a SODICK™ molding machine sold by PlustechInc. of Schaumburg, Ill. In embodiments, the extruder includes eitherone or two members known in the art as “screws” disposed within theinterior volume, known in the art as a “barrel”. In embodiments, thescrews have a right circular cylindrical shape overall, and furtherinclude one or more protruding thread members referred to as “flights”.In some embodiments the extruder is a single screw extruder, defined asincluding one screw movably disposed within the barrel for rotation ofthe cylinder around the axis thereof, for lateral movement of thecylinder along the axis thereof, or a combined movement comprising bothrotation and lateral movement. In other embodiments the extruder is atwin screw extruder, defined as including two screws movably disposedwithin the barrel in substantially parallel and proximal relationshipwith respect to each other, further where each screw is movably disposedwithin the barrel for rotation of the cylinder around the axis thereof,for lateral movement of the cylinder along the axis thereof, or acombined movement comprising both rotation and lateral movement. Thescrews of a twin screw extruder are further arranged so that the actionof the screws when turned in counter-rotating fashion define a designedmixing and transportation pattern of a molten thermoplastic polymerdisposed within the barrel.

In embodiments, the extruder is further adapted and designed to receivea solid thermoplastic polymer. In embodiments, the barrel of theextruder is further adapted and designed to receive a solidthermoplastic polymer by including an inlet situated near a first end ofthe extruder and adapted to add a solid thermoplastic polymer to thebarrel. The solid thermoplastic polymer is added to the inlet in anysuitable format, for example beads, pellets, powders, ribbons, orblocks, which are all familiar formats to those of skill. Inembodiments, the extruder includes second, third, or even fourth orhigher numbers of inlets designed and adapted for adding or introducingone or more additional materials comprising one or more solids, liquids,or gases to the interior volume of the extruder, further for mixing theone or more additional materials with the thermoplastic polymer. Theinterior volume of the extruder is adapted for receiving, containing,and melting a thermoplastic polymer and optionally one or moreadditional materials; and subjecting the thermoplastic polymer and theoptional one or more additional materials to heat, shear and mixing toform a molten mixture, while contemporaneously transporting the moltenmixture in a direction generally proceeding from the first end thereofto a second end thereof. In embodiments where the extruder is a singlescrew extruder or a twin screw extruder, the shear, mixing, andtransportation is accomplished by rotating the screw or counter-rotatingtwo screws.

In embodiments the extruder interior volume, or a portion thereof, issurrounded or partly surrounded by one or more heat sources. Heatsources suitably adapted for heating the interior volume of an extruderinclude, in various embodiments, heated water jackets, heated oiljackets, electrical resistance heaters, open or jacketed flames, oranother heat source. The heat source is operable to raise a temperaturein the interior volume of the extruder. The temperature is suitablyselected by the operator for melting a thermoplastic polymer and/ormaintaining a desired temperature within a portion of the interiorvolume of the extruder. In embodiments, an extruder is adapted toinclude more than one heat source, wherein the heat sources areindependently operable to enable one of skill to provide a range oftemperature “zones” within the interior volume. Additional temperaturezones may be included in some extruders in association with adding oneor more materials to an inlet thereof or dispensing one more materialsfrom an outlet thereof. In embodiments, temperatures within the one ormore temperature zones are set by the operator for increased control andoptimization of melting, mixing, shearing, and transportation of thethermoplastic polymer and optionally one or more additional materials.

The extruder is conventionally designed and adapted to apply andmaintain a pressure within the interior volume thereof during theheating, mixing and transportation of a molten mixture. In embodiments,the extruder is designed and adapted to apply and maintain a firstpressure within the interior volume or barrel during the heating, mixingand transportation of a molten mixture. In embodiments, the pressureinside the barrel during the heating, mixing and transportation of amolten pneumatic mixture is sufficient to prevent or substantiallyprevent leakage of molten pneumatic mixture from the barrel. Inembodiments, the pressure within the barrel is sufficient to prevent amolten pneumatic mixture from developing pneumatoceles when atemperature within the barrel exceeds the critical temperature of thepneumatogen source. In embodiments, the pressure within the barrel issubstantially sufficient to prevent a molten pneumatic mixture fromdeveloping pneumatoceles when a temperature within the barrel exceedsthe critical temperature of the pneumatogen source. In such embodimentsdescribed in this paragraph, “substantially” refers to inadvertentleaking of material or inadvertent loss of pressure from the barrel dueto manufacture, age, or manner of use of the extruder and/or the screwas is familiar to one of skill. Further in such embodiments“substantially” in the context of “sufficient to prevent a moltenpneumatic mixture from developing pneumatoceles”, means that a smallpercentage, such as up to 10% of the pneumatogen may inadvertently formpneumatoceles while the pressure is maintained on a molten pneumaticmixture; but that it is the goal of the operator to maintain sufficientpressure to prevent pneumatoceles from forming.

In embodiments, the barrel of the extruder includes a collection regionfor collecting an amount of a molten mixture in preparation fordispensing the molten mixture from the extruder. The mass of the moltenmixture is selected by the user. In embodiments, the molten mixture is amolten pneumatic mixture. In such embodiments, the term of art used todescribe the collecting of a mass of a molten pneumatic mixture in acollection region of the barrel of the extruder is referred to as“building a shot”. As will be understood by one skilled in the art ofinjection molding, to build a shot, a mass of a molten pneumatic mixtureis collected by transporting the molten pneumatic mixture from the firstend toward the second end of the extruder—that is, toward and into thecollection region—by the rotation of the screw or screws (or anothermixing element) and by further allowing the molten pneumatic mixture toaccumulate in the collection region until the entirety of the desiredmass of molten pneumatic mixture is collected and is disposed in thecollection region of the barrel. The collection region is situatedbetween the screw or screws and the second end of the extruder and is inpressurized communication with the remainder of the barrel.

In conventional injection molding to form thermoplastic polymer foams, amass of molten pneumatic mixture, or “shot”, is collected or “built” inthe collection region by transporting the molten pneumatic mixturetoward and into the collection region by the rotation of the screw orscrews (or another mixing element). A shot is said to be built when theentire selected mass of molten pneumatic mixture is disposed within thecollection region. One of skill will appreciate that the foregoingdescription of melt mixing apparatuses, such as the mechanical elementsand features of an extruder or other melt mixing apparatus, and furtherthe foregoing description of methods of making and collecting moltenpneumatic mixtures in a shot, is in accord with conventional apparatusesand methods of using such apparatuses to make molten pneumatic mixturesand to build shots thereof.

In accord with these known methods and apparatuses, a shot of moltenpneumatic mixture is conventionally prevented or substantially preventedfrom developing pneumatoceles while present in the barrel, includingduring the mixing, heating, transporting, and collecting and furtherwhile disposed within the collection region. Conventionally, when adesired shot is collected in the collection region, a gate or doorsituated between the collection area and an outlet situated on thesecond end of the extruder is opened, providing fluid connection fromthe barrel to the outlet to dispense the shot from the extruder. In someembodiments when the gate or door is opened, a mechanical plunger isapplied to urge the molten pneumatic mixture from the barrel and throughthe outlet. In embodiments a screw or screws are suitably employed inlateral movement in a direction toward the second end of the extruder,which in turn urges the molten pneumatic mixture from the collectionregion of the barrel and through the outlet.

We have found that after building a shot of a molten pneumatic mixturein the collection region of an extruder, it is advantageous to form,provide, or define an expansion volume in the collection region of theextruder, wherein the defining is accompanied by a pressure drop in thecollection region; allowing a period of time to pass after the defining,referred to herein as the expansion period; and dispensing the shot fromthe extruder after the expansion period. The shot in such embodiments isdispensed in the form of a molten polymer foam. In embodiments, theexpansion volume is defined proximal to the shot disposed within thecollection region of the extruder. In embodiments, the shot is not mixedor subjected to applied shear or extension while the expansion volume isin the process of being defined. In embodiments, the shot is nottransported during the expansion period. In embodiments, the shot isallowed to stand, or reside, undisturbed or substantially undisturbed inthe collection region during the expansion period. In any of theforegoing embodiments, the shot may be heated during the expansionperiod; however, in some embodiments, no heat is added to the shotduring the expansion period.

After the expansion period has elapsed or passed, a molten polymer foammay be dispensed from the second end of the extruder. The molten polymerfoam includes a plurality of pneumatoceles. Without being limited bytheory, we believe that the pneumatoceles form when the molten pneumaticmixture is subjected to the expanded volume and accompanying pressuredrop (second pressure). In accord with known principles of physics, theformation of the pneumatoceles is likely caused by the defining of theexpanded volume and concomitant pressure drop in the collection regionof the barrel, together with the expansion period in which thepneumatoceles form by action of the pneumatogen. In some embodiments,defining the expansion volume after building the shot results insuperior properties attributable to the molten polymer foam that isdispensed. Stated differently, we have found that forming a moltenpneumatic mixture under pressure, followed by lowering the pressure andconcomitantly forming a defined volume prior to dispensing the mixture(such as into a mold cavity), results in a molten polymer foam that uponcooling provides solidified polymer foam articles having unexpected andhighly beneficial physical properties.

We have discovered that molten polymer foams dispensed from the extruderin accord with the foregoing methods obtain significant technicalbenefits. These benefits are observed in the solidified polymer foamsthat result from cooling the molten polymer foam to a temperature belowa melt transition temperature of the thermoplastic polymer. Thestructure of articles made using the molten polymer foam dispensed froman extruder after the expansion period is different both macroscopicallyand microscopically from polymer foams made by conventional methods; andexhibit superior properties suitable for structural members, forexample. The polymer foam articles made using the methods, apparatuses,and materials described herein that are characterized as having acontinuous thermoplastic matrix throughout the entirety thereof, and aplurality of pneumatoceles distributed throughout the entirety of thepolymer foam article. This characterization is true for articles havingthicknesses greater than 2 cm, volumes greater than 1000 cm³, orthicknesses greater than 2 cm in addition to volumes greater than 1000cm³, of between 1000 cm³ to 5000 cm³, or even more than 5000 cm³; andfurther for articles comprising a volume of more than 1000 cm³ and athickness of more than 2 cm, a volume between 1000 cm³ and 5000 cm³ anda thickness of more than 2 cm, or a volume of more than 5000 cm³ and athickness of more than 2 cm.

In embodiments, the defining of the expansion volume in a single screwextruder is suitably achieved by moving the screw laterally toward afirst end of the extruder and away from the collection region of theextruder where the shot is collected. In embodiments, the defining ofthe expansion volume in a twin screw extruder is achieved by moving bothscrews laterally toward a first end of the extruder and away from theregion of the extruder where the shot is collected. The lateral movingis optionally accompanied by rotation of the screw or screws. That is,the one or two screws may be rotated during the lateral moving or therotation may be stopped during the lateral moving. It will beappreciated that the defining of the expansion volume by lateralmovement of the one or two screws is advantageously selected by theoperator of an extruder to provide a selected expansion volume. That is,the distance of the lateral movement of the screw or screws is suitablyselected by the operator to define the selected expansion volume.

Accordingly, in embodiments, the expansion volume is targeted by theoperator to add sufficient volume to the collection region toaccommodate the total expected molten polymer foam volume; or somepercentage of thereof. The total expected molten polymer foam volume ofa shot may be calculated based on the amount of thermoplastic polymerand pneumatogen source plus any additional materials added to build theshot, further assuming all of the pneumatogen source will contribute toformation of pneumatoceles in the molten polymer foam to be obtained.Those of skill will understand that industrially obtained pneumatogensources are supplied with information suitable to calculate the totalexpected molten polymer foam volume based on the amount of pneumatogensource added to make the shot, and other processing conditions. Inembodiments, the expansion volume is the difference between the shotvolume and the expected molten polymer foam volume. In embodiments, theexpansion volume is targeted to provide between 10% and 100% of thetotal expected molten polymer foam volume in the collection region, forexample between 15% and 100%, or between 20% and 100%, or between 25%and 100%, or between 30% and 100%, or between 35% and 100%, or between40% and 100%, or between 45% and 100%, or between 50% and 100%, orbetween 55% and 100%, or between 60% and 100%, or between 65% and 100%,or between 70% and 100%, or between 75% and 100%, or between 80% and100%, or between 85% and 100%, or between 90% and 100%, or between 10%and 95%, or between 10% and 90%, or between 10% and 85%, or between 10%and 80%, or between 10% and 75%, or between 10% and 70%, or between 10%and 65%, or between 10% and 60%, or between 10% and 55%, or between 10%and 50%, or between 10% and 45%, or between 10% and 40%, or between 10%and 35%, or between 10% and 30%, or between 10% and 25%, or between 10%and 20%, or between 10% and 15%, or between 15% and 20%, or between 20%and 25%, or between 25% and 30%, or between 30% and 35%, or between 35%and 40%, or between 40% and 45%, or between 45% and 50%, or between 50%and 55%, or between 55% and 60%, or between 60% and 65%, or between 65%and 70%, or between 70% and 75%, or between 75% and 80%, or between 80%and 85%, or between 85% and 90%, or between 90% and 95%, or between 95%and 100% of the difference between the shot volume and the expectedmolten polymer foam volume. In still other embodiments, the expansionvolume is between 100% and 300% of the difference between the shotvolume and the expected molten polymer foam volume, such as 100% to 105%or 100% to 110% or 100% to 115% or 100% to 120% or 105% to 110% or 110%to 115% or 115% to 120% or 120% to 125% or 120% to 150% or 150% to 200%or 200% to 250% or 250% to 300% of the difference between the shotvolume and the expected molten polymer foam volume.

After the expansion volume is defined, a period of time is allowed topass, or elapse, prior to dispensing the molten polymer foam from theextruder. In embodiments the period of time is referred to as theexpansion period. In some embodiments, during the expansion period nomixing, transporting, shearing, or other physical manipulation oradditional volume changes are carried out within the collection regionduring the expansion period. Instead, in such embodiments the shot isallowed to stand within collection region during the expansion period.At the end of the expansion period, a molten polymer foam is dispensedfrom the extruder outlet. In embodiments, the molten polymer foam isdispensed into a mold cavity, and the molten polymer foam is cooled to atemperature below a melt transition of the thermoplastic polymer toobtain a solidified polymer foam article.

In embodiments, the expansion period is selected by the operator to beabout 5 seconds to 600 seconds, depending on the mass of the sample,pneumatogen source and amount, and any additional materials present inthe shot. In embodiments, the expansion period is 5 seconds to 600seconds, or 5 seconds to 500 seconds, or 5 seconds to 400 seconds, or 5seconds to 300 seconds, or 20 seconds to 600 seconds, or 20 seconds to500 seconds, or 20 seconds to 400 seconds, or 20 seconds to 300 seconds,or 10 seconds to 200 seconds, or 20 seconds to 200 seconds, or 30seconds to 200 seconds, or 40 seconds to 200 seconds, or 50 seconds to200 seconds, or 5 seconds to 190 seconds, or 5 seconds to 180 seconds,or 5 seconds to 170 seconds, or 5 seconds to 160 seconds, or 5 secondsto 150 seconds, or 5 seconds to 140 seconds, or 5 seconds to 130seconds, or 5 seconds to 120 seconds, or 5 seconds to 110 seconds, or 5seconds to 100 seconds, or 5 seconds to 90 seconds, or 5 seconds to 80seconds, or 5 seconds to 70 seconds, or 5 seconds to 60 seconds, or 5seconds to 50 seconds, or 5 seconds to 40 seconds, or 5 seconds to 30seconds, or 5 seconds to 20 seconds, or 5 seconds to 10 seconds, or 10seconds to 15 seconds, or 15 seconds to 20 seconds, or 20 seconds to 25seconds, or 25 seconds to 30 seconds, or 30 seconds to 35 seconds, or 35seconds to 40 seconds, or 40 seconds to 45 seconds, or 45 seconds to 50seconds, or 50 seconds to 55 seconds, or 55 seconds to 60 seconds, or 60seconds to 70 seconds, or 70 seconds to 80 seconds, or 80 seconds to 90seconds, or 90 seconds to 100 seconds, or 100 seconds to 110 seconds, or110 seconds to 120 seconds, or 120 seconds to 130 seconds, or 130seconds to 140 seconds, or 140 seconds to 150 seconds, or 150 seconds to160 seconds, or 160 seconds to 170 seconds, or 170 seconds to 180seconds, or 180 seconds to 190 seconds, or 190 seconds to 200 seconds,or 200 seconds to 250 seconds, 250 seconds to 300 seconds, or 300seconds to 350 seconds, or 350 seconds to 400 seconds, or 400 seconds to450 seconds, or 450 seconds to 500 seconds, or 500 seconds to 550seconds, or 550 seconds to 600 seconds.

Using the foregoing methods results in formation a molten polymer foamthat obtains several significant technical benefits, described insections below, when the molten polymer foam is cooled to a temperaturebelow a melt temperature of the thermoplastic polymer to yield asolidified polymer foam. The polymer foam articles are generallycharacterized as monolithic articles having a continuous polymer matrixdefining a plurality of pneumatoceles dispersed throughout the entiretyof the article. In embodiments the polymer foam articles areparticularly characterized as having a continuous polymer matrixdefining a plurality of pneumatoceles dispersed in a surface region ofthe article, wherein the surface region is defined as the area of thearticle between the article surface (the polymer foam-air interface) anda distance 500 microns interior from the surface

A representative embodiment of an apparatus usefully employed to carryout the foregoing methods is shown in FIG. 1A. FIG. 1A is a schematicdiagram of an exemplary single screw injection molding apparatus 20 inaccordance with disclosed embodiments herein, that is useful to performthe methods described herein to make molten polymer foams and polymerfoam articles also disclosed herein. As shown in FIG. 1A, injectionmolding system 20 includes barrel 21, attached to motor or drive section24 and mold section 26. Barrel 21 includes first end 21 a, second end 21b, and defines hollow interior barrel portion 22. Barrel portion 22further defines nozzle 36 proximal to barrel second end 21 b. Screw 30is disposed within barrel portion 22 and comprises screw tip portion 34.Screw 30 is operably coupled to the motor section 24 for rotation ofscrew 30 around the central axis thereof; or for lateral movementindicated by arrow Z. Lateral movement of screw 30 may be in a directiongenerally from barrel first end 21 a toward barrel second end 21 b; orin a direction from barrel second end 21 b toward barrel first end 21 a.Lateral movement of screw 30 in either direction is optionally furthercoupled with rotational movement. Screw 30 further includes one or moreflights 31 which are mixing elements for mixing and transportingmaterials present within barrel portion 22 generally from barrel firstend 21 a toward barrel second end 21 b. Screw 30 is disposed withinbarrel portion 22 in pressurably sealed relationship therein, to enablepressures in excess of atmospheric pressure to be maintained withinbarrel portion 22, by screw flights 31 within the barrel 21 and furtherby situation of check valve 32. Shutoff valve 37 is connected to barrel21 near second end 20 b, and is operable to control a fluid connection,a pressurized connection, or both between nozzle 36 and mold section 26.Check valve 32 disposed within barrel portion 22 and surrounding screw30 is operable to prevent backpressure from urging materials residing inbarrel portion 22 toward barrel first end 21 a and thus provides apressurably sealed, fluidly sealed, or pressurably fluidly sealedrelationship between shutoff valve 37 and check valve 32.

Further with regard to FIG. 1A, mold section 26 includes two moldsections 38 as shown. Mold sections 38 are removably joined together todefine cavity 39. In some embodiments, one or more of the mold sections38 are movable to allow for ejection of a solidified polymer foamarticle therefrom. In some embodiments, the mold sections 38 aresituated in touching relation to each other; in other embodiments moldsections 28 are spaced apart by a gap.

In embodiments, the methods disclosed herein are suitably carried outusing an apparatus such as system 20 shown in FIGS. 1A-1B. In FIG. 1A, aselected mass of mixture 42A comprising a selected amount ofthermoplastic polymer, pneumatogen source, and optionally one or moreadditional materials is added to barrel section 22 through inlet 28, asindicated by arrow A. In some embodiments, the pneumatogen source is apneumatogen and inlet 28 or another inlet (not shown) is a gas inlet inpressurized connection with barrel section 22; and the pneumatogen isadded to the gas inlet at a selected pressure, while non-gaseousmaterials are added to inlet 28. During addition of mixture 42A tobarrel portion 22 through inlet 28, motor 24 is operable to rotate screw30. The rotation of screw 30 transports and mixes the mixture 42A to thescrew tip 34. A heat source (not shown) is suitably employed to add heatto mixture 42A within the barrel portion 22. Motor 24 rotates screw 30to transport mixture 42A present in barrel portion 22 in a directiongenerally proceeding from first end 21 a of barrel 21 towards second end21 b, until reaching screw tip 34. Additionally, the rotation of screw30 provides mixing of mixture 42A during the transportation. As mixture42A is transported and mixed by rotation of screw 30, heating elementsor heating bands (not shown) proximal to barrel portion 22 operate toheat mixture 42A. Multiple heating zones may be present proximal tobarrel portion 22 to vary the temperature inside barrel portion 22between first end 21 a and second end 21 b of barrel 21. Duringtransportation, screw 30 rotating within barrel portion 22 is operableto mix mixture 42A; and heat is added to the mixture as it istransported, thereby raising the temperature of the mixture above amelting point of the thermoplastic polymer to transform mixture 42A intomolten pneumatic mixture 42B at least by reaching second end 21 b ofbarrel 21. Additionally, disposition of screw 30 within barrel portion22, further wherein flights 31 are in contact with barrel 21 duringrotation of screw 30; combined with check valve 32, shutoff valve 37 ina closed position, or both provides a pressurably sealed relationshipwithin barrel portion 22 whereby the molten pneumatic mixture 42B ispresent in barrel portion 22 under a pressure in excess of atmosphericpressure. The pressure within barrel portion 22 is sufficient to preventor substantially prevent pneumatocele formation, even if the pneumatogensource is above its critical temperature.

Further, rotation of screw 30 operates to transport the pressurizedmolten pneumatic mixture toward screw tip 34, transporting or buildingup a selected mass of pressurized molten pneumatic mixture 42B within acollection region 40 of barrel portion 22. Collection region 40 isdefined as the region within the volume of barrel portion 22 extendingbetween check valve 32 and shutoff valve 37 in FIG. 1A, further as aregion of barrel portion 22 situated along X distance of barrel 21. Aselected mass or “shot” of pressurized molten pneumatic mixture 42B iscollected, or built up, in collection region 40 of barrel portion 22.Pressure within the collection region 40 is sufficient to prevent orsubstantially prevent pneumatocele formation in the molten pneumaticmixture. In embodiments, the shot substantially fills collection region40.

Building the shot of molten pneumatic mixture 42B is achieved usingconventional methods familiar to those of skill. Conventional and knownvariations in methods and materials employed to build a shot forinjection molding are encompassed by the methods described herein. Oncea shot is built, it may be subjected to the methods disclosed herein toobtain all the technical benefits disclosed herein with respect toforming polymer foams and polymer foam articles. For example, to form ashot, methods such the MUCELL® high-pressure process employed by TrexelInc. of Wilmington, Mass. are suitably employed, wherein addition ofpneumatogen source as a gas directly to an extruder with pressurizedmixing to prevent or substantially prevent pneumatocele formation isfollowed by shot collection. Various patent art and trade publicationsfurther describe specialized melt mixing and conveying designs forobtaining molten pneumatic mixtures and forming a shot, such asspecialized screw designs for mixing and backflow patterns and the like;any of these may be usefully employed in conjunction with the foregoingshot formation methods and apparatuses to form a shot as describedherein and collect the shot under a pressure within a collection regionof a melt mixing apparatus.

Once a shot is formed and collected in a collection region, an expansionvolume is defined therein, further wherein the expansion is accompaniedby a drop in a pressure in the collection region and proximal to theshot. Accordingly, FIG. 1A depicts a molten pneumatic mixture apparatus20 wherein screw 30 is positioned to collect a shot of in collectionregion 40. The shot includes the selected mass of molten pneumaticmixture 42B and is disposed under a pressure within collection region40. At this stage of the process, further relative to FIG. 1A, FIG. 1Bdepicts apparatus 20 wherein screw 30 is positioned to define anexpansion volume 44 within collection region 40. In somewhat moredetail, FIG. 1B shows screw 30 in a position resulting from lateralmovement of screw 30 toward barrel first end 21 a; that is, screw 30 isretracted in FIG. 1B relative to FIG. 1A. Retraction and the resultingpartial displacement of screw 30 from collection region 40 defines anexpansion volume 44 within collection region 40 and further causes apressure to drop within collection region 40. In some embodiments,rotation of screw 30 is halted before the retracting. In someembodiments, rotation of screw 30 is halted during the retracting, orafter the retracting is completed. The retraction distance of screw 30,that is, the distance of lateral movement of screw 30 toward barrelfirst end 21 a is selected by the operator to provide a suitableexpansion volume 44.

In some embodiments represented in FIG. 1B, expansion volume 44 isselected by the operator to provide collection region 40 having a totalvolume that matches the total expected molten polymer foam volume of theshot; in such embodiments, the total volume in collection region 40after adding expansion volume 44 is the total expected molten polymerfoam volume of the molten pneumatic mixture 42B of FIG. 1B. In otherembodiments, expansion volume 44 is selected by the operator to providecollection region 40 having a total volume that is a percentage of thetotal expected molten polymer foam volume of a molten pneumatic mixtureor shot residing in collection area 40; that is, the total volume incollection region 40 after adding expansion volume 44 equals about 50%to 120% of the total expected molten polymer foam volume. In someembodiments, expansion volume is set to provide a total volume in thecollection region to accommodate 100% of the total expected moltenpolymer foam volume. The total expected molten polymer foam volume of ashot may be calculated based on the amount of thermoplastic polymer andpneumatogen source plus any additional materials added to build theshot, further assuming all of the pneumatogen source contributes toformation of pneumatoceles in the molten polymer foam to be obtained.

After retracting screw 30 to define expansion volume 44 as shown in FIG.1B, a period of time, referred to as the “expansion period” is allowedto elapse or pass while the shot is held within collection region 40 asshown in FIG. 1B, specifically wherein collection region 40 includesexpansion volume 44. The expansion period is selected by an operator tobe between 5 seconds and 200 seconds. In embodiments, during theexpansion period the shot is allowed to stand undisturbed orsubstantially undisturbed within collection region 40. In embodiments,“undisturbed” means that the shot is not subjected to any processescausing mixing, shearing, or transporting (flow) of the shot during theexpansion period. In embodiments, “substantially undisturbed” means thatthe shot is not purposefully perturbed by mixing, shearing, ortransporting processes carried out during the expansion period but e.g.heat differentials, leakage, and other manufacturing issues may lead toinadvertent stress or strain to the shot residing in the collectionregion during the expansion period.

After the expansion period has elapsed, nozzle shutoff valve 37 as shownin FIG. 1B is opened and a molten polymer foam is dispensed from barrel22. In embodiments as shown in FIGS. 1A-1B, the molten polymer foamflows into cavity 39. The dispensing may be pressurized dispensing bymechanical means such as plunging using lateral movement of the screw,or by applying a pressurized gas to the collection region, but applyingpressure is not necessary to dispense the molten polymer foam in someembodiments. In embodiments, pressure at nozzle 36 as shown in FIGS.1A-1B during dispensing of the molten polymer foam is 1 psi to 20 psi inexcess of gravity, such as 3 psi to 20 psi, 5 psi to 20 psi, 7 psi to 20psi, 10 psi to 20 psi, 15 psi to 20 psi, 1 psi to 15 psi, 1 psi to 10psi, 1 psi to 7 psi, 1 psi to 5 psi, 2 psi to 5 psi, 5 psi to 10 psi, 10psi to 15 psi, or 15 psi to 20 psi, without adding external sources ofpressure such as by plunging the molten polymer foam using additionallateral movement of the screw 30 toward barrel second end 21 b in FIGS.1A-1B. In embodiments, the dispensing is accomplished by maintainingfluid connection between nozzle 36 and cavity 39. In some suchembodiments the fluid connection is further a pressurized connection.

Once disposed within cavity 39 defined by mold portions 38 shown inFIGS. 1A-1B, the molten polymer foam is cooled or allowed to cool untilit reaches a temperature below a melt transition of the thermoplasticpolymer, such as the temperature present in ambient conditions of thesurrounding environment. In some embodiments where an expansion volumeis set to provide a total volume in the collection region that is lessthan 100% of the total expected molten polymer foam volume,pneumatoceles may continue to nucleate and/or develop (grow in size)after the molten polymer foam is dispensed and before the temperaturecools sufficiently to reach a melt transition temperature of thethermoplastic polymer. Cooling of the molten polymer foam isaccomplished using conventional methods for cooling of injection moldedarticles and includes immersing the mold in a liquid coolant having aset temperature, or spraying the mold with a liquid coolant, such asliquid water; impinging an air stream onto the mold; ambient aircooling; and the like without limitation.

In an alternate embodiment of the foregoing methods, apparatus 20configured as shown in FIG. 1B is employed to form a molten polymerfoam. FIG. 1B shows screw 30 in a position resulting from lateralmovement of screw 30 toward barrel first end 21 a; that is, screw 30 isretracted in FIG. 1B relative to FIG. 1A. Retraction and the resultingpartial displacement of screw 30 from collection region 40 defines anexpansion volume 44 within collection region 40 and further causes apressure to drop within collection region 40. Apparatus 20 configurationas shown in FIG. 1B is employed to mix, heat, and transport moltenpneumatic mixture 42B toward second end 21 b of barrel 21 insubstantially the same way as described above. Additionally, dispositionof screw 30 within barrel portion 22, further wherein flights 31 are incontact with barrel 21 during rotation of screw 30; combined with checkvalve 32, shutoff valve 37 in a closed position, or both provides apressurably sealed relationship within barrel portion 22 whereby themolten pneumatic mixture 42B is present in barrel portion 22 under apressure in excess of atmospheric pressure. The pressure within barrelportion 22 is sufficient to prevent or substantially preventpneumatocele formation, even if the pneumatogen source is above itscritical temperature. However, in this alternative embodiment the moltenpneumatic mixture is transported through check valve 32 and intocollection region 40 further appended by the expansion volume 44.

It is an advantage of the presently disclosed methods that conventionalmaterials and apparatuses for extrusion and injection molding are usefulfor carrying out the methods. No specialized equipment or materialrequirements are needed to carry out the disclosed methods. Thus, anythermoplastic polymer or mixture thereof that is useful for injectionmolding and/or for forming polymer foams, is usefully combined with anyindustrially useful pneumatogen source using conventional technologysuch as a standard injection molding apparatus, optionally together withone or more additional materials as selected by the operator of theapparatus.

In embodiments, thermoplastic polymers useful in conjunction with themethods, apparatuses, and articles described herein include anythermoplastics or mixtures thereof that are known in the industry to beuseful for injection molding, or injection molding of polymer foamarticles; and mixtures of such polymers. Useful polymers arecharacterized as having a melt flow viscosity suitable for use ininjection molding, such as in shot formation. As such, the thermoplasticpolymers may include a degree of crosslinking that is thermoreversibleor that does not otherwise prevent a sufficient viscous melt flow forinjection molding processes.

In embodiments, thermoplastic polymers useful in conjunction with themethods, apparatuses, and articles described herein include olefinicpolymers such as polyethylene, polypropylene, poly α-olefins and variouscopolymers and branched/crosslinked variations thereof including but notlimited to low density polyethylene (LDPE), high density polyethylene(HDPE), linear low density polyethylene (LLDPE), thermoplasticpolyolefin elastomer (TPE), ultra-high molecular weight polyethylene(UHMWPE), and the like; polyamides (PA), polyimides (PI), polyesterssuch as polyester terepthalate (PET) and polybutyene terepthalate (PBT),polyhydroxyalkanoates (PHA) such as polyhydroxybutyrate (PHB),polycarbonates (PC), poly (lactic acid)s (PLA),acrylonitrile-butadiene-styrene copolymers (ABS), polystyrenes,polyurethanes including thermoplastic polyurethane elastomers (PU, TPU),polycaprolactones, polyvinyl chlorides (PVC), copolymers oftetrafluoroethylene, polyethersulfones (PES), polyacetals, polyaramids,polyphenylene oxides (PPO), polybutylenes, polybutadienes, polyacrylatesand methacryates (acrylics), ionomeric polymers (SURLYN® and similarionically functionalized olefin copolymers), poly ether-amide blockcopolymers (PEBAX®), polyaryletherkeytones (PAEK), polysulfones,polyphenylene sulfides (PPS), polyamide-imide copolymers, poly(butylenesuccinate)s, cellulosics, polysaccharides, and copolymers, alloys,admixtures, and blends thereof are usefully employed in conjunction withthe methods described herein, without limitation.

Regarding unlimited use of polymer blends and mixtures, we have foundmixed stream recycled plastics are useful in embodiments as thethermoplastic polymer. Thus in embodiments ocean waste plastics aremixed streams of polymeric waste harvested from oceans and beaches, andhaving exemplary content of 10%-90% polyolefin content, 10%-90% PETcontent, 1%-25% polystyrene content, and 1% to 50% unknown polymercontent. Such mixed plastic streams and waste plastic streams, notlimited to those collected from oceans and beaches, are similarlyusefully to form molten polymer foams and polymer foam articles usingthe methods and apparatuses described herein.

Pneumatogen sources are widely available in the industry and conditionsuseful to deploy pneumatogens during melt mixing are well understood andbroadly reported. Accordingly, any pneumatogen source useful forinjection molding, reaction injection molding, or other methods ofmaking of polymer foams, is useful herein to form the molten polymerfoams and solidified polymer foam articles in accordance with themethods, apparatuses, and polymer foam articles described herein.Pneumatogens useful in connection with the methods and apparatusesdescribed herein include air, CO₂, and N₂, either as encapsulated withina thermoplastic in the form of beads, pellets, and the like or in latentform, wherein a chemical reaction generates CO₂ or N₂ when heated withinthe melt mixing apparatus. Such chemical reactions are suitablyexothermic or endothermic without limitation regarding their use inconjunction with the methods and apparatuses disclosed herein. Suitablepneumatogen sources include sodium bicarbonate, compounds based on apolycarboxylic acid such as citric acid, or a salt or ester thereof suchas sodium citrate or the trimethyl ester of sodium citrate; mixtures ofsodium bicarbonate with a polycarboxylic acid such as citric acid;sulfonyl hydrazides including p-toluene sulfonyl hydrazide (p-TSH) and4,4′-oxybis-(benzenesulfonyl hydrazide) (OBSH), pure and modifiedazodicarbonamides, semicarbazides, tetrazoles, and diazinones. In any ofthe foregoing, the pneumatogen source is optionally further encapsulatedin a carrier resin designed to melt during the heating, mixing, andcollection of a shot.

In embodiments, useful pneumatogen sources include commerciallyavailable compositions such as HYDROCEROL® BIH 70, HYDROCEROL® BIHCF-40-T, or HYDROCEROL® XH-901, all available from Clariant AG ofSwitzerland; FCX 7301, available from RTP Company of Winona, Minn.; FCX27314, available from RTP Company of Winona, Minn.; CELOGEN® 780,available from CelChem LLC of Naples, Fla.; ACTAFOAM® 780, availablefrom Galata Chemicals of Southbury, Conn.; ACTAFOAM® AZ available fromGalata Chemicals of Southbury, Conn.; ORGATER MB.BA.20, available fromADEKA Polymer Additives Europe of Mulhouse, France; ENDEX1750™,available from Endex International of Rockford, Ill.; and FOAMAZOL™ 57,available from Bergen International of East Rutherford, N.J.

In some embodiments, the pneumatogen source is a pneumatogen, whereinthe pneumatogen is applied as a gas to a melt mixing apparatus, such asan apparatus similar to the extruder shown in FIGS. 1A-1B. In suchembodiments the gas is caused to dissolve within the thermoplasticpolymer by direct pressurized addition to and mixing within the meltmixing apparatus. In some embodiments the gas becomes a supercriticalfluid by pressurization, either prior to or contemporaneously withdissolution into the molten thermoplastic polymer. Applying apneumatogen directly to an injection molding apparatus is referred toindustrially as the MUCELL® process, as employed by Trexel Inc. ofWilmington, Del. Specialized equipment is required for this process,such as a regulated, pressurized fluid connection from a gas reservoir(tank, cylinder etc.) to the inlet of an extruder apparatus to form apressurized relationship with the barrel as the thermoplastic polymer isalso added to the barrel and melted. Where such specialized equipment isavailable, a pneumatogen is usefully employed as the pneumatogen sourcein conjunction with the methods described herein by direct applicationof the pneumatogen to the thermoplastic polymer and one or moreadditional materials to form a molten pneumatic mixture.

The pneumatogen source is added to the thermoplastic polymer, and anyoptionally one or more additional materials, in an amount that targets aselected density reduction of the thermoplastic polymer, in accordancewith conventional art associated with desirable polymer foam density andoperation of pneumatogens and pneumatogen sources to form thermoplasticpolymer foams. The amount of the pneumatogen source added to thethermoplastic polymer is not particularly limited; accordingly, we havefound that up to 85% density reduction is achieved without the use ofpolymer or glass bubbles or the like, to provide a polymer foam articlehaving the unique and surprising characteristics reported below andfurther having a targeted density reduction of up to 85%. As usedherein, “density reduction” means a percent mass reduction in a polymerfoam article compared to the same article without adding a pneumatogen(source) to make the article (that is, a polymer article excluding orsubstantially excluding pneumatoceles). Thus, in embodiments the moltenpolymer foams and the polymer foam articles described herein suitablyexclude glass or polymer bubbles, while providing a selected densityreduction of up to 85%, for example 30% to 85%, such as 35% to 85%, 40%to 85%, 45% to 85%, 50% to 85%, 55% to 85%, 60% to 85%, 65% to 85%, 70%to 85%, 75% to 85%, 30% to 35%, 35% to 40%, 40% to 50%, 50% to 55%, 55%to 60%, 60% to 65%, 65% to 70%, 70% to 75%, 75%, to 80%, or 80% to 85%.Including glass or polymer bubbles further extends the available densityreduction of a polymer foam article made in accord with the methodsherein. In some embodiments greater than 85% density reduction may beachieved. The polymer foam articles benefitting from the densityreduction nonetheless are characterized as having a continuous polymermatrix throughout with pneumatoceles dispersed therein, including moldedarticles having a volume greater than 1000 cm³, of between 1000 cm³ to5000 cm³, or even more than 5000 cm³; and molded articles a volume ofmore than 1000 cm³ and a thickness of more than 2 cm, a volume between1000 cm³ and 5000 cm³ and a thickness of more than 2 cm, or a volume ofmore than 5000 cm³ and a thickness of more than 2 cm.

As mentioned above, the amount of the pneumatogen source added to thethermoplastic polymer is not particularly limited; accordingly, we havefound that up 70% of the total volume of a polymer foam articlecomprises pneumatoceles. The total volume of the pneumatoceles as apercent of the total volume of the polymer foam article is referred toas the “void fraction” of the article; thus, void fraction of up toabout 70% is achieved without including polymer or glass bubbles or thelike, to provide a polymer foam article having the unique and surprisingcharacteristics reported below and further having a targeted voidfraction of up to 70% of the volume of the polymer foam article. Thus,in embodiments the molten polymer foams and the polymer foam articlesdescribed herein suitably exclude glass or polymer bubbles, whileproviding a void fraction of up to 70%, for example 5% to 70%, such as10% to 70%, 15% to 70%, 20% to 70%, 25% to 70%, 30% to 70%, 35% to 70%,40% to 70%, 45% to 70%, 50% to 70%, 55% to 70%, 60% to 70%, 5% to 10%,10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%, 30% to 35%, 35% to 40%,40% to 50%, 50% to 55%, 55% to 60%, 60% to 65%, or 65% to 70%. Includingglass or polymer bubbles further extends the available void fraction ofa polymer foam article made in accord with the methods herein. In someembodiments greater than 70% void fraction may be achieved. The polymerfoam articles having 70% void fraction are nonetheless are characterizedas having a continuous polymer matrix throughout with pneumatocelesdispersed therein, including molded articles having a volume greaterthan 5000 cm³, thickness greater than 2 cm, or both volume greater than5000 cm³ and thickness greater than 2 cm.

In some embodiments, the thermoplastic polymer and a pneumatogen sourceare admixed prior to applying the admixture to a melt mixing apparatusfor heating and mixing. In other embodiments, the thermoplastic polymerand a pneumatogen source are added separately to a melt mixingapparatus, such as by two different inlets or ports available for addingmaterials to the melt mixing apparatus. In still other embodiments, asolid mixture including both a thermoplastic polymer and a pneumatogensource are added as a single input to a melt mixing apparatus forheating and mixing.

In embodiments, one or more additional materials are included or addedto a melt mixing apparatus along with the thermoplastic polymer andpneumatogen source; such additional materials are suitably mixed oradmixed with the thermoplastic polymer, the pneumatogen source, or both;or the one or more additional materials are added separately, such as byin individual port or inlet to a melt mixing apparatus. Examples ofsuitable additional materials include colorants (dyes and pigments),stabilizers, brighteners, nucleating agents, fibers, particulates, andfillers. Specific examples of some suitable materials include talc,titanium dioxide, glass bubbles or beads, thermoplastic polymerparticles, fibers, beads, or bubbles, and thermoset polymer particles,fibers, beads, or bubbles. Additional examples of suitable materialsinclude fibers such as glass fibers, carbon fibers, cellulose fibers andfibers including cellulose, natural fibers such as cotton or woolfibers, and synthetic fibers such as polyester, polyamide, or aramidfibers; and including microfibers, nanofibers, crimped fibers, shreddedor chopped fibers, phase-separated mixed fibers such as bicomponentfibers including any of the foregoing mentioned polymers, and thermosetsformed from any of the foregoing polymers. Further examples of suitableadditional materials are waste materials, further shredded or chopped asappropriate and including woven or nonwoven fabrics, cloth, or paper;sand, gravel, crushed stone, slag, recycled concrete and geosyntheticaggregates; and other biological, organic, and mineral waste streams andmixed streams thereof. Further examples of suitable additional materialsare minerals such as calcium carbonate and dolomite, clays such asmontmorillonite, sepiolite, and bentonite, micas, wollastonite,hydromagnesite/huntite mixtures, synthetic minerals, silica agglomeratesor colloids, aluminum hydroxide, alumina-silica composite colloids andparticulates, Halloysite nanotubes, magnesium hydroxide, basic magnesiumcarbonate, precipitated calcium carbonate, and antimony oxide. Furtherexamples of suitable additional materials include carbonaceous fillerssuch as graphite, graphene, graphene quantum dots, carbon nanotubes, andC₆₀ buckeyballs. Further examples of suitable additional materialsinclude thermally conductive fillers such as boronitride (BN) andsurface-treated BN.

In embodiments, one or more additional materials are included or addedto a melt mixing apparatus along with the thermoplastic polymer andpneumatogen source in an amount of about 0.1% to 50% of the mass of thethermoplastic polymer, for example 0.1% to 45%, 0.1% to 40%, 0.1% to35%, 0.1% to 30%, 0.1% to 25%, 0.1% to 20%, 0.1% to 15%, 0.1% to 10%,0.1% to 9%, 0.1% to 8%, 0.1% to 7%, 0.1% to 6%, 0.1% to 5%, 0.1% to 4%,0.1% to 3%, 0.1% to 2%, 0.1% to 1%, 1% to 50%, 2% to 50%, 3% to 50%, 4%to 50%, 5% to 50%, 6% to 50%, 7% to 50%, 8% to 50%, 9% to 50%, 10% to50%, 11% to 50%, 12% to 50%, 13% to 50%, 14% to 50%, 15% to 50%, 20% to50%, 25% to 50%, 30% to 50%, 35% to 50%, 40% to 50%, 45% to 50%, 0.1% to2%, 2% to 5%, 5% to 10%, 10% to 15%, 15% to 20%, 20% to 25%, 25% to 30%,30% to 35%, 35% to 40%, 40% to 45%, or 45% to 50% of the mass ofthermoplastic polymer added to the melt mixing apparatus to form a shot.

Accordingly, in melt mixing apparatuses that are not extruders, it willbe understood by one of skill that the following method will result in amolten polymer foam possessing the significant technical benefitsdescribed in sections below. A method of forming and collecting a moltenpolymer foam includes the following: heating and mixing a thermoplasticpolymer and a pneumatogen source to form a molten pneumatic mixture,wherein the temperature of the molten pneumatic mixture exceeds thecritical temperature of the pneumatogen source and a pressure applied tomolten pneumatic mixture is sufficient to substantially preventformation of pneumatoceles; collecting a selected amount of the moltenpneumatic mixture in a collection region; defining an expansion volumein the collection region proximal to the molten pneumatic mixture thatresults in a pressure drop; maintaining the expansion volume for anexpansion period of time; and collecting a molten polymer foam from thecollection region. In embodiments, the molten pneumatic mixture isundisturbed or substantially undisturbed during the expansion period.

In some embodiments, collecting the molten polymer foam includesapplying the molten polymer foam to a cavity defined by a mold; andcooling the molten polymer foam below a melt temperature of thethermoplastic polymer to obtain a polymer foam article. In embodimentswhere the molten polymer foam is applied to the cavity of a mold, thecooled polymer foam article obtains the shape and dimensions of themold, further wherein polymer foam is characterized as a continuouspolymer matrix having pneumatoceles distributed throughout the entiretyof the article. In embodiments, the molten polymer foam is applied to amold cavity by allowing the molten polymer foam to flow and enter a moldcavity by gravitational force; in some such embodiments the flow isunimpeded and is allowed to fall into an open cavity. In otherembodiments, the molten polymer foam is applied under pressurized flowto a forming element. In embodiments the molten polymer foam isdelivered to a mold cavity by fluid connection thereto from a nozzle orother means of delivery of molten polymer foam from a collection regionof a melt mixing apparatus.

For example, in embodiments, an extruder is adapted and designed todispense a molten mixture from an outlet into a forming element, whichis a mold defining a cavity therein, and designed and adapted to receivea molten polymer mixture, such as a molten pneumatic mixture. Inembodiments the forming element is a mold configured and adapted toreceive a molten thermoplastic polymer dispensed from an outlet, furtherwherein a mold is characterized as generally defining a void or cavityhaving the selected shape and dimensions of a desired article.

In embodiments, dispensing from an extruder is accomplished bymechanical plunging, by applying a gaseous pressure from within thebarrel of the extruder, or a combination thereof. In other embodiments,an outlet, valve, gate, nozzle, or door to the collection region issimply opened after the expansion period has passed, and the moltenpolymer foam is allowed to flow unimpeded through the outlet; the moltenflow is then directed to a cooling or other processing apparatus, or themolten flow is allowed to pour into a forming element. In otherembodiments, the forming element is fluidly connected to the outlet andis further designed and adapted to be filled with a molten mixture sothat the molten mixture obtains a selected shape when cooled andsolidified. In some embodiments, the forming element is fluidlyconnected to the extruder outlet such that a pressure is maintainedbetween the collection region, the outlet, and the forming element ormold. Any conventional thermoplastic molding or forming processassociated with injection molding of polymer articles, such as polymerfoam articles, is suitably employed to mold the molten polymer foamsdescribed herein.

In embodiments where the molten polymer foam is allowed to flowunimpeded through the outlet, or is plunged under a pressure from theoutlet without further impedance of flow, the molten flow eventuallyimpinges on a surface, such as a surface generally perpendicular to thedirection of the molten flow. We have observed that the flow under suchcircumstances then obtains a generally cylindrical (coiling) and planar(folding) pattern during continued molten flow, such as reported byBatty and Bridson, “Accurate Viscous Free Surfaces for Buckling,Coiling, and Rotating Liquids” Symposium on Computer Animation, Dublin,July 2008. In embodiments, the molten polymer foam is allowed to flow,or is “poured” unimpeded from the outlet of a melt mixing apparatus andinto a mold that is configured as an open container. In embodiments theopen container mold is completely filled with molten polymer foam; inother embodiments the open container mold is partially filled withmolten polymer foam.

In some embodiments related to the coiled molten flow described above, amolten flow substantially free of shear, or a substantially linearmolten flow, or a molten flow that is substantially linear and free ofshear is provided by fluid connection between the outlet of the extruderand into a mold cavity. In some such embodiments, the molten flow mayobtain a coiled molten flow, either by impinging on a perpendicularsurface thereof or by flowing down a substantially vertical wall or sideof a mold cavity and collecting at the bottom of the mold cavity. Aschematic representation of one such an embodiment is shown in FIG. 41,which shows a variation of the extruder of FIGS. 1A-1B wherein mold 26of apparatus 20 is situated on a substantially horizontal surface 100.In reference to elements as shown in FIGS. 1A-1B, there is no shutoffvalve 37 at distal end 21 b of barrel 21; instead, in FIG. 41,collection region 40 extends to a mold valve 137 situated proximal tomold cavity 39 defined within mold 26. Thus, mold valve 137 is operableto define collection region 40, or to provide an outlet for dispensing amolten polymer foam to mold cavity 39 via a substantially linearhorizontal flow 110. Mold valve 137 is situated a height H abovehorizontal surface 100, and a height H2 above the floor or bottom 120 ofmold 26 as situated on horizontal surface 100. In reference to FIG. 41,mold valve 137 is selectively opened to provide fluid connection betweencollection region 40 and mold cavity 39. Thus, mold valve 137 isselectively opened to provide a substantially linear horizontal flow 110of molten polymer foam entering mold cavity 39. Upon entering moldcavity 39, the linear flow flows downward over the distance H2, and insome embodiments obtains a coiled molten flow as it proceeds to fillmold cavity 39. Other related variations of the methods and apparatusesare contemplated to provide a coiled molten flow as described herein.

In embodiments, upon cooling and removing a polymer foam article from anopen container or a mold situated such as shown in FIG. 41, the coilingand folding flow pattern is visible at the surface of the article. Anexample of such a visible flow pattern may be seen in e.g. FIGS. 2-2 and2-4. Upon cryogenic fracturing and microscopic inspection of theinterior of polymer foam articles formed using the coiled and foldingflow, the interior of the article is free of or substantially free offlow patterns, interfaces, or other evidence of coils and folds. Forexample, cryogenic fracturing of such polymer foam articles does notresult in fracturing at any discernible interface between coils andfolds; and both macroscopic and microscopic inspection of the interiorof such polymer foam articles obtains a homogeneous appearance withrespect to flow patterns. The physical properties of such polymer foamarticles are consistent with the physical properties obtained bysubjecting the molten polymer foam to a directed fluid flow, via fluidconnection between an outlet of a melt mixing apparatus and a mold, orsubjecting the molten polymer foam to pressurized directed fluid flow.

In some embodiments, the methods herein include substantially filling amold with the molten polymer foam formed in accordance with theforegoing described methods, then cooling the molten polymer foam toform a solidified polymer foam; and in embodiments further removing thesolidified polymer foam article from the mold. In embodiments, thecooling is cooling to a temperature below a melt transition of thethermoplastic polymer. In embodiments, the cooling is cooling to atemperature in equilibrium with the ambient temperature of thesurrounding environment. In some embodiments the mold further includesone or more vents for pressure equalization in the mold during fillingthereof with molten polymer foam, but in other embodiments no vents arepresent. After cooling, a polymer foam article may be removed from themold for further modification or use.

In accord with any of the foregoing description, Table 1 provides usefulbut non-limiting examples of processing conditions employed to make amolten polymer foam using a conventional single screw extruder typereaction injection molding apparatus, further by employing one or morerepresentative thermoplastic polymers and a citric acid-basedpneumatogen source as indicated.

TABLE 1 Representative thermoplastic polymers and conditions useful formaking and molding molten polymer foams. Polymer Samples High ImpactPolyamide 6 / Thermoplastic Surlyn 30% LDPE / Variable Polystyrene PBTPC/ABS 15% Talc Elastomer Ionomer 70% PP PMMA Blowing Agent % 2 (Endo) 3(Endo) 3 (Endo) 2 (Endo) 2 (Endo) 2 (Endo) 2 (Endo) 3% (Endo) +Hydrocerol BIH 70 0.5% (endothermic) OR (Exothermic) Hydrocerol XH-901(exodothermic) Mold cavity dimension 4 × 4 × 2 4 × 4 × 2 4 × 4 × 2 6″sphere 4 × 4 × 2 4 × 4 × 2 3″ Sphere 4 × 4 × 2 (in) Shot volume (cc) 545545 545 1856 545 545 252 545 Shot size (cm³ ) 4026.3 4294.7 295.0 983.2327.7 278.6 98.3 180.3 Decompression volume 131.1 409.7 1065.2 819.4163.9 49.2 49.7 163.9 (cm³ ) Melt temperature (° C.) 213 227 221 265 221150 360 226 Clamp tonnage 10 10 15 20 10 17 14 10 Cooling time (s) 120120 90 160 320 500 120 160 Decomp time (s) 60 80 60 100 60 50 56 100Hold pressure (MPa) 0 0 0 0 0 0 0 0 Hold time (s) 0 0 0 0 0 0 0 0Injection speed (cm³/s) 0.066 0.098 0.041 0.066 0.057 0.066 0.082 0.049Mold temperature (° C.) 10 43 29 44 30 10 20 35 Screw speed (m/s) 0.150.11 0.21 0.15 0.15 0.15 0.12 0.09 Specific backpressure 6.90 12.41 7.5910.34 8.97 8.97 6.90 5.17 (MPa) Injection pressure (MPa) 31.03 37.9341.38 34.48 48.28 129.66 13.79 14.45 Final part density (g/cc) 0.4560.571 0.597 0.454 0.594 0.476 0.327 0.482

In embodiments, the dimensions of molds usefully employed to form thepolymer foam articles made using the methods, and materials disclosedherein include molds that define cavities that may be filled by a singleshot of molten polymer foam, or a series of cavities that may be filledby a single shot of molten polymer foam. As such, the size of the moldcavity is limited only by the size of the shot that can be built in themelt mixing apparatus employed by the user. Representative mold cavitieshaving volumes of up to 1×10⁵ cm³ are useful for making large parts suchas automobile cabin or exterior parts, I-beam construction parts, andother large plastic items suitably employing a polymer foam. Further,the shape of the mold cavities are not particularly limited and may becomplicated in terms of overall shape and even surface patterns andfeatures, for example shapes recognizable as dumbbells, tableware,ornamental globes with raised geographical features, human or animal orinsect shapes, framework or encasement shapes for framing or encasinge.g. electronic articles, appliances, automobiles, and the like, shapesfor later disposing and fitting screws, bolts, and othernon-thermoplastic items into or through the polymer foam article; andthe like are all suitable mold shapes for molding a polymer foam articleas described herein. In some embodiments the cavity includes a thicknessgradient of up to 300% as to one or more regions of the cavity.

In accord with any of the foregoing description, Table 2 provides usefulbut non-limiting examples of mold cavity volumes and dimensions of moldsuseful to mold the molten polymer foams, either by pressurized flow orby unimpeded flow of the molten polymer foam into the mold.Additionally, larger mold volumes, such as up to 100,000 cm³ or largerare useful where shot mass is suitably increased.

TABLE 2 Representative mold cavity volumes and dimensions useful to moldthe molten polymer foams. Part Cavity Volume (cc) 3″ diameter sphere231.00 6″ diameter sphere 1,856.66 9″ diameter sphere 6,243.47 18″diameter sphere 50,038.52 Duck Body 4,771.10 Duck Head 812.80 12″ × 12″× 1″ Plate 2,359.74 4″ × 4″ × 2″ Brick 545.69 4″ × 4″ × 4″ Block1,091.38 12″ × 12″ × 12″ Block 28,316.84 17″ × 4″ × 1″ Plate 1,114.3211″ × 4″ × 2″ Plate 1,442.06 2″ × 2″ × 0.5″ Plate 32.77 2″ × 2″ × 2″Block 131.10 2.625″ × 5.625″ × 1″ Plate 241.97 1″ × 1″ × 2″ Plate 32.77

Any the methods, processes, uses, machines, apparatuses, or individualfeatures thereof described above are freely combinable with each otherto form polymer foams and polymer foam articles having unique andsurprising characteristics. Thus, in embodiments, a polymer foam articleis formed using the foregoing described methods, materials, andapparatuses. The polymer foam article is a discrete, monolithic objectmade by forming or molding a molten polymer foam in accordance with anyof the methods and materials disclosed above as well as variationsthereof which are combinable in any part and in any manner to form amolten polymer foam as described above.

Accordingly, terminology used to refer to the methods, materials, andapparatuses in the foregoing discussion are used below to refer toarticles made using one or more methods, materials, and apparatusesencompassed in the foregoing discussion.

In embodiments, any combination of the foregoing methods results information of a polymer foam article comprising, consisting essentiallyof, or consisting of a continuous thermoplastic polymer matrix defininga plurality of pneumatoceles. The continuous thermoplastic polymermatrix comprises, consists of, or consists essentially of a solidthermoplastic polymer, that is, the thermoplastic polymer is present ata temperature below a melt transition thereof. In embodiments, thecontinuous thermoplastic polymer matrix further includes one or moreadditional materials dispersed in the solid thermoplastic polymer.

The polymer foam articles obtain density reductions, based on thedensity of the thermoplastic polymer and any other materials added toform the polymer foam, of a selected percent based on the amount ofpneumatogen source added to the shot. In embodiments, a densityreduction of 30%, 40%, 50%, 60%, 70% and even up to 80% to 85% densityreduction, as selected by the user. In embodiments, up to 85% densityreduction is achieved solely by the presence of pneumatocelesdistributed discontinuously in the polymer matrix. In embodiments, thepolymer foam articles exclude hollow particulates such as polymer orglass bubbles added to the shot prior to forming the polymer foamarticle using the methods and apparatuses described herein.

Further in conjunction with reduced density, as mentioned above thepolymer foam articles herein are characterized as having a continuousthermoplastic polymer matrix throughout the entirety thereof orsubstantially throughout the entirety thereof. We have found that largepolymer foam articles may be suitably formed from the molten polymerfoams disclosed herein to include a continuous polymer matrix defining aplurality of pneumatoceles. “Large” articles are those having volumes of1000 cm³ or more, for example 2000 cm³ or more, 3000 cm³ or more, 4000cm³ or more, or 5000 cm³ or more, or any volume between 1000 cm³ and5000 cm³; and including volumes up to 10,000 cm³, up to 20,000 cm³, upto 50,000 cm³, or even up to 100,000 cm³ or greater. Thus, large polymerfoam articles may be suitably formed to include a continuous polymermatrix defining a plurality of pneumatoceles throughout the entiretythereof. The volume of the article is limited only by the size of themold cavity and the size of the shot that can be collected in the meltmixing apparatus. In embodiments, a large article is formed from asingle shot dispensed from a single outlet of a melt mixing apparatus,that is, without splitting of the molten polymer foam flow to multiplesimultaneous distribution pipes, nozzles, or other methods of directingmultiple molten streams simultaneously into a single mold cavity.

Additionally, we have found that thick polymer foam articles may besuitably formed to include a continuous polymer matrix defining aplurality of pneumatoceles. Thickness as used herein refers to straightline distance through the interior of a polymer foam article between anytwo points on the surface thereof “Thick” articles are defined as havinga thickness of 2 cm or more, such as 3 cm, 4 cm, 5 cm, 6 cm, 7 cm, 8 cm,9 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, 45 cm, or even 50cm or more. In some embodiments, a polymer foam article is formed usingthe methods and materials described herein that is characterized asbeing both large and thick, further wherein the large, thick polymerfoam article is nonetheless characterized as having a continuous polymermatrix defining a plurality of pneumatoceles throughout the article. Inembodiments, a large, thick article is formed from a single shotdispensed from a single outlet of a melt mixing apparatus, that is,without splitting of the molten polymer foam flow to multiplesimultaneous distribution pipes, nozzles, or other methods of directingmultiple molten streams simultaneously into a single mold cavity.

The manufacture of large, thick, or large and thick polymer foamarticles is problematic in the industry due to the cooling gradient ofthe molten foam after it is dispensed into a cavity having suchdimensions. The interior of such articles tends to cool very slowly, andsome of the thermoplastic polymer disposed in the mold cavity may remainabove a melt temperature thereof, allowing significant coalescence ofpneumatoceles to occur before the thermoplastic solidifies (reaches atemperature below a melt transition thereof). In sharp contrast, we havefound that large articles, thick articles, and large, thick articles aresuitably formed using the methods, materials, and apparatuses disclosedherein, further wherein the formed polymer foam article is characterizedby a continuous polymer matrix having pneumatoceles distributedthroughout the article. The slower-cooling interior of larger articlesshow minimal or no evidence of pneumatocele coalescence during cooling.The pneumatoceles remain intact or substantially intact during coolingof the molten polymer foam and do not coalesce during cooling, resultingin a continuous polymer matrix regardless of size, thickness, or volumeof the polymer foam article formed.

This feature of the polymer foam articles described herein is surprisingand unexpected: the methods of the prior art result in foams that tendto undergo pneumatocele coalescence during cooling. Accordingly, amolten polymer foam of the conventional art, situated in the interiorvolume of a mold, may cool so slowly that pneumatoceles are able tocompletely coalesce, and consequently the interior of a large or thickarticle formed using conventional polymer foaming methods may obtainvery large gaps or even a completely collapsed structure in the interiorthereof. In sharp contrast, the molten polymer foams formed according tothe present methods do not undergo substantial pneumatocele coalescenceor collapse of the continuous polymer matrix during cooling of moltenpolymer foam. Accordingly, large and thick polymer foam articles with acontinuous polymer matrix throughout are achieved using the methods,materials, and apparatuses described herein.

The continuous polymer matrix, as a structural feature of the polymerfoamed articles in accord with the foregoing methods, apparatuses, andmaterials is characterized as present throughout the entirety of thepolymer foamed article, including the surface region thereof. Thesurface region may be suitably characterized as the interior area of apolymer foam article that is 500 microns or less from the surface. Thesurface region as defined herein is a portion of the area of a foamedarticle conventionally referred to the “skin layer”, which is a regionfree or pneumatoceles or substantially free of pneumatoceles in polymerfoam articles made using conventional methods.

Conventionally formed foam articles include a skin layer that is atleast as thick as the surface region, that is, 500 microns thick; butoften the skin layer is much thicker and may proceed as far as 1 mm, 1.5mm, 2 mm, 2.5 mm, even 3 mm from the surface of the article. However,the polymer foam articles formed using the presently disclosed methodsobtain a true foam structure from the surface thereof and throughout theentire thickness and volume thereof. In embodiments, microscopicinspection reveals evidence of pneumatoceles on the surface of thepolymer foam articles formed using the conditions, processes, andmaterials disclosed herein. Accordingly, the methods disclosed hereinobtain unexpected results in terms of the continuous nature of thepolymer matrix structure throughout the entirety of the polymer foamarticle, in any direction, and in every region thereof including withinthe interior of very large and/or thick polymer foam articles and alsoat the surface and in the surface region of the article.

The Examples below include analyses of the surface region of multiplepolymer foam articles made using the methods disclosed herein and thatexhibit this continuous foam structure. Macroscopically, a polymer foamarticle made using the methods disclosed herein may appear to have askin layer: that is, the surface region of the article can appear to bedifferent from the interior region of the article. However, we havefound that in sharp contrast to a skin layer characterized by theabsence of pneumatoceles, the surface regions of polymer foam articlesmade by the present methods include a plurality of compressedpneumatoceles. Macroscopically the compressed pneumatoceles create anappearance suggesting a skin layer; however, microscopic inspectionreveals that the visually apparent difference arises from a “flattened”or compressed disposition of the continuous polymer matrix near thesurface of the article.

Thus, for example as seen in FIG. 17 and FIG. 18, there is a gradualtransition from spherical to compressed pneumatoceles moving towards thesurface of polymer foam article formed by employing the conditions,processes, and materials disclosed herein. Thus, in embodiments, asurface region of a polymer foamed article made using the methodsdisclosed herein includes a plurality of compressed pneumatoceles. Inembodiments, the compressed pneumatoceles are present in the surfaceregion of a polymer foam article made using the methods disclosedherein. In some such embodiments, compressed pneumatoceles are presentwithin an interior area of a polymer foam article that is 500 microns orless from the surface. In some such embodiments, compressedpneumatoceles are present within an interior area of a polymer foamarticle that is as far as 2 cm from the surface. Compressedpneumatoceles are defined as pneumatoceles having a circularity of lessthan 1, wherein a circularity value of zero represents a completelynon-spherical pneumatocele, and a value of 1 represents a perfectlyspherical pneumatocele. In embodiments, pneumatoceles having circularityof less than 0.9 are observed in the surface region of foamed polymerarticles, further wherein 10% to 90%, or 10% to 80%, or 10% to 70%, or10% to 60%, or 10% to 50%, or 10% to 40%, or 10% to 30%, or 10% to 20%,or 20% to 80%, or 20% to 70%, or 20% to 60%, or 20% to 50%, or 20% to40%, or 20% to 30%, or 30% to 70%, or 30% to 60%, or 30% to 50%, or 30%to 40% of the pneumatoceles in the surface region have a circularity of0.9 or less. In embodiments, an average circularity in the surfaceregion of the foamed polymer articles is 0.70 to 0.95, such as 0.75 to0.95, or 0.80 to 0.95, or 0.85 to 0.95, or 0.90 to 0.95, or 0.70 to0.90, or 0.70 to 0.85, or 0.70 to 0.80, or 0.70 to 0.75, or 0.70 to0.75, or 0.75 to 0.80, or 0.80 to 0.85, or 0.85 to 0.90, or 0.90 to0.95.

In embodiments, compressed pneumatoceles are present in a polymer foamarticle more than 500 microns from the surface thereof. For example, inembodiments, compressed pneumatoceles are present up to 1 mm from thesurface of a polymer foam article, or up to 2 mm, 3 mm, 4 mm, 5 mm, 6mm, 7 mm, 8 mm, 1 cm, or more from the surface thereof. In someembodiments the region of compressed pneumatoceles in the polymer foamarticle corresponds to 0.01% to 70% of the total volume of the article,for example 0.1% to 70%, or 0.5% to 70%, or 1% to 70%, or 2% to 70%, or3% to 70%, or 4% to 70%, or 5% to 70%, or 6% to 70%, or 7% to 70%, or 8%to 70%, or 9% to 70%, or 10% to 70%, or 15% to 70%, or 20% to 70%, or30% to 70%, or 40% to 70%, or 50% to 70%, or 60% to 70%, or 0.01% to60%, or 0.01% to 60%, or 0.01% to 50%, or 0.01% to 40%, or 0.01% to 30%,or 0.01% to 20%, or 0.01% to 10%, or 0.01% to 9%, or 0.01% to 8%, or0.01% to 7%, or 0.01% to 6%, or 0.01% to 5%, or 0.01% to 4%, or 0.01% to3%, or 0.01% to 2%, or 0.01% to 1%, or 0.01% to 0.1% of the total volumeof the article.

FIGS. 12 and 14 shows a plot of average pneumatocele size and averagepneumatocele count versus average pneumatocele circularity for twopolymer foam articles made using the presently disclosed methods.Quantitative analysis of pneumatocele size and distribution reveals aninverse relationship between the average pneumatocele size andpneumatocele circularity, and an inverse relationship between theaverage pneumatocele size and the number of pneumatoceles.

FIG. 18 additionally shows visual evidence that pneumatoceles arepresent to the surface of the polymer foam articles formed using themethods, materials, and apparatuses as described herein. FIG. 18additionally shows visual evidence that a plurality of compressedpneumatoceles are present substantially 500 microns from the surface ofthe polymer foam articles formed using the methods, materials, andapparatuses as described herein. In this sense, the polymer foamarticles presently disclosed obtain a significant difference from foamarticles of the prior art. While the “skin layer”, or first 500 micronsof thickness of a foam article made by conventional processes include nopneumatoceles or substantially no pneumatoceles, it is a feature of theprior art foam articles generally that the pneumatoceles are sphericalwherever they are located. Thus, at the thickness in a conventional foamarticle where pneumatoceles are observed, they are generally spherical,having circularity near or about 1. Compressed pneumatoceles are notformed using conventional methodology to make foamed articles, andtherefore no distribution of pneumatocele circularity is observed insuch conventional foam articles. Further, pneumatoceles are not evenformed in the first 500 microns thickness of a foam article made byconventional processes, so no comparisons regarding pneumatoceles can bedrawn as to the surface region of the foamed polymer articles asdescribed herein and the foamed articles made using conventionalinjection molding methods.

Further, conditions, processes, and materials disclosed herein aresuitably optimized to form polymer foam articles having differentphysical properties depending on the targeted end use or application.For example, the density of a polymer foam article is suitably varied asa function of expansion volume. By lowering the expansion volume, thedensity of the resulting polymer foam article is decreased in agenerally linear fashion, for example as shown in FIG. 5. Also as can beseen from FIG. 5, increasing the expansion period of time causes adenser polymer foam article to form. Such conditions and othervariables, all within the scope of the conditions, methods, andmaterials disclosed herein are suitably used to vary the physicalproperties of the polymer foam articles that result.

In one variation of conditions, processes, and materials disclosedherein, a molten polymer foam is suitably dispensed by splitting theflow of molten polymer foam into 2, 3, 4, or more pathways heading tomultiple molds or mold sections to form multiple polymer foam articlesfrom a single shot. In another variation of conditions, processes, andmaterials disclosed herein, two shots are used to fill a single mold,wherein the first shot is different from the second shot in terms of thethermoplastic polymer content or ratio of mixed polymers, thepneumatogen source, the one or more additional materials optionallyincluded, density, void fraction, depth of the region of compressedpneumatoceles, or some other material or physical property difference.

In another variation of conditions, processes, and materials disclosedherein, a polymer foam article made using the methods disclosed hereinwas subjected to fastener pull out testing according to ASTM D6117. Thepolymer foam articles obtain superior pull out strength over foamarticles made using conventional foaming methods. Further, the polymerfoam articles formed using the materials, methods, and apparatusesdisclosed herein require no pre-drilling, tapping or engineering of thefastener location.

In yet another variation of conditions, processes, and materialsdisclosed herein, a polymer foam article made using the methodsdisclosed herein was subjected to ballistic testing. Using the guidanceof National Institute of Justice (NIJ) “Ballistic Resistance of BodyArmor NIJ Standard-0101.06”, a series of 3 inch thick polymer foamarticles were formed from poly ether-amide block copolymers (PEBAX®),linear low density polyethylene (LLDPE), and polypropylene using acitric acid based pneumatogen source. Polymer foam articles made usingall three of these thermoplastic polymers were found to stop 0.22 LRhandgun bullets, passing NIJ Level I; and were found to stop 9 mm LUGER®handgun bullet, passing NIJ Levels II and IIA.

Experimental Section

The following examples are intended to further illustrate this inventionand are not intended to limit the scope of the invention in any manner.Examples 1 and 11 were conducted on an Engel Duo 550 Ton injectionmolding machine (available from Engel Machinery Inc. of York, Pa., USA).Examples 2-4 were conducted on a Van Dorn 300 injection molding machine(available from Van Dorn Demag of Strongsville, Ohio, USA). Unlessotherwise indicated, the remaining examples were conducted on an EngelVictory 340 Ton injection molding machine (available from EngelMachinery Inc. of York, Pa., USA).

In the Examples herein, “cc” means “cubic centimeter” or “cubiccentimeters” (cm³), “sec” means “second” or “seconds”.

Standard Foam Molding and MFIM

In the Examples herein, two direct injection expanded foam moldingtechniques were employed termed herein “standard foam molding” and“molten foam injection-molding” (“MFIM”).

In standard foam molding, the following general procedure was used: A) Amixture was prepared by blending a polymer (which may be in the form ofpellets, powder, beads, granules and the like) with a foaming agent(blowing agent) and any other additives such as a filler. The mixturewas introduced to the injection unit, and the rotating injection unitscrew moved the mixture forward in the injection unit barrel, thusforming a heated fluid material in accordance with normal injectionmolding processes. B) A set volume of the material was dosed to thefront of the barrel of the injection unit by rotation of the screw, thusmoving the set volume from the feed zone to the front of the screw.During this feed step, the screw was rotated to translate the meltedmixture forward into the space in the barrel between the screw and thenozzle, thereby providing the set volume. C) The melted mixture wasinjected into the mold cavity by forward translation of the screw and/orrotation of the screw.

In the molten foam injection-molding (MFIM) process, the followinggeneral procedure was used: A) A mixture was prepared by blending apolymer (which may be in the form of nurdles, pellets, powder, beads,granules and the like) with a chemical foaming agent, and any otheradditives such as a filler. The mixture was introduced to the injectionunit, and the rotating injection unit screw moved the material forwardin the injection unit barrel, thus forming a heated fluid material inaccordance with normal injection molding processes. B) A set volume ofthe material was dosed to the front of the barrel of the injection unitby rotation of the screw, thus moving the set volume from the feed zoneto the front of the screw. During this feed step, the screw was rotatedto move the material between the screw and the nozzle, thereby providingthe set volume. C) Once the material had been moved to the front of thescrew, in a step termed herein “decompression”, the screw was movedbackwards away from the nozzle without or substantially without rotationso as to avoid moving more of the material to the front of the screw.

A space free of the mixture between the screw and the nozzle was createdwithin the barrel, the intentional space having a volume termed herein“decompression volume”. D) The material sat in the barrel between thescrew and the nozzle for a period of time, termed herein the“decompression time”. During the decompression time, the material foameddue to a pressure drop created by the space added in step (C). E) Themolten foam was injected into the mold cavity by forward translation ofthe screw and/or rotation of the screw.

Example 1

Two parts were foam molded using a blend of low-density polyethyleneblended with 2% by weight Hydrocerol® BIH 70 foaming agent availablefrom Clariant AG of Muttenz, Switzerland. Molding was conducted using anEngel Duo 550 Ton injection molding machine (available from EngelMachinery Inc. of York, Pa., USA). The mold cavity was (approximately)spherical in shape of diameter six inches (15.24 cm). A first part wasmolded using a standard foam molding process, and a second part wasmolded using an MFIM process. An aluminum mold having a cold sprue andrunner system feeding a 6-inch diameter sphere cavity was employed forboth parts. The melt delivery system for each part was the same, as weremost of the processing conditions. The process settings for the MFIMprocess and standard foam molding processes used as a control aredetailed in TABLE 3. From each process, parts were made of approximatelyequivalent mass.

TABLE 3 Settings for Example 1; Equivalent mass study Standard FoamMolding Process MFIM Barrel temperatures182/182/182/174/163/154/161/121/49 (° C.) Mold temperature (° C.) 10Injection speed (cc/s) 655.5 Back pressure (kPa) 17237 Decompression(cc) — 164 Screw speed (cm/sec) 15.24 Cooling time (sec) 160 Hold time(sec) 30 — Hold pressure (kPa) 8963 — Shot weight (g) 328.9 331.9

The first and second parts were photographed. FIG. 2-1 is a photographicimage of the first part, molded using the standard foam molding process.As seen in the image, the standard foam process did not yield a partthat filled the mold cavity, and the part did not match the shape of thespherical cavity of the mold.

FIG. 2-2 is a photographic image of the second part, molded using theMFIM process. As seen in the image, the MFIM process yielded a part thatentirely or substantially filled the spherical mold cavity and the partmatched or substantially matched the shape of the spherical cavity ofthe mold.

The first part molded using the standard foam molding process was cutinto two pieces. FIGS. 2-3 and 2-5 are photographic images of one of thepieces of the part made according to the standard foam molding process.As seen in the images, the first part contained a large hollow cavity.

The second part molded according to the MFIM process was cut into twopieces. FIGS. 2-4 and 2-6 are photographic images of one of the piecesof the second part. As seen in the images, the second part lacked thelarge hollow cavity of the standard foam process part. The MFIM part hada cell structure throughout.

Example 2

Two parts were formed by foam injection molding, a Part A in accordancewith a standard foam molding process, and a Part B in accordance with anMFIM process. In both processes, LDPE/talc pellets were dry-blended withfoaming agent and mixed during loading into the molding machine.

For Part B, a mixture of low-density polyethylene (LDPE), talc, andHydrocerol® BIH 70 was formed and fed into a Van Dom 300 injectionmolding machine to provide a polymer shot inside the barrel. After theshot accumulated in the front of the screw, the screw was translatedbackwards away from the injection nozzle without rotation in accordancewith the MFIM method to create a space between the screw and the nozzle,the space having a decompression volume. Then, the mixture foamed intothe space prior to injection into the mold.

The same procedure was used for Part A except that after the shotaccumulated in front of the screw, the screw was not backed away fromthe nozzle, i.e. decompression volume was zero. The shot was metered tofill the mold cavity under standard foam molding conditions with atarget of 10% weight reduction relative to solid part.

TABLES 4-7 below show the polymer, mold, machine, and processingsettings used in Example 2.

TABLE 4 Material Composition Weight % Polymer: LDPE 82% Filler: Talc 15%Foaming agent: Hydrocerol ® BIH 70  3%

TABLE 5 Baseline Mold Parameters Block Mold (2 × 4 × 4 inch) ASTM Mold(5.08 × 10.16 × 10.16 cm) Mold cavity volume (cc) 524.39 Sprue Volume(cc)  17.39 Total Volume (cc) 541.78

TABLE 6 Common Settings for Producing “Zero Decompression” and MFIMParts Barrel Temperatures (° C.) 154|185|177|166 Mold Temperature (° C.)20 Back pressure (kPa) 0 Screw Speed (rpm) 165 Screw Rotate Delay time(sec) 100 Hold time (sec) 10 Injection Velocity (cc/sec) 394

TABLE 7 Independent Settings Shot Details Part A Part B Polymer mass (g)456.2 189.4 Polymer volume in barrel (cc) 486.3 162.12 Decompressionvolume (cc) 0 231.57 Total molten shot size (cc) 486.297 393.69 Coolingtime (sec) 800 160

Each of Parts A and B was cut in half to reveal a cross section. FIG. 3Aand FIG. 3B show the resulting cross sections of Part A and Part Brespectively. As shown in FIG. 3A, Part A had a thick outer regionextending nearly 0.8 inches (20.3 mm) from the surface, indicating thatmore than 50% of the molded part was completely solid. The density ofPart A was 0.84 g/cc.

FIG. 3B shows a cross section of Part B molded according to the MFIMprocess using the settings shown in TABLE 4 and TABLE 5. As seen in FIG.3B, Part B had a foam structure that includes a distribution of cellsizes and shapes. A solid, unfoamed outer region is nearly absent fromPart B. The density of Part B was 0.35 g/cc.

A sphere cavity mold was used to form a further two parts, Part C andPart D, by foam injection molding. The same mixture composition of LDPE,talc, Hydrocerol® BIH 70 was used to form Parts C and D. Part C was madeby the MFIM process, Part D by the standard foam molding process. Bothprocesses produced a spherical or approximately spherical part having asix inch (15.24 cm) diameter. Parts C and D were cut through the middle(widest part) into two pieces to expose a cross section of the part.FIG. 4A is a photographic image of a cross section of Part C made by theMFIM process (471 g, required cooling time 160 seconds). FIG. 4B is aphotographic image of the cross section of Part D molded using standardfoaming process targets (1360 g, required cooling time 800 seconds).

Similar results were obtained as with the block mold. Part C madeaccording to the MFIM process showed cells throughout the part, whereasPart D made according to the standard foam molding process showed aregion adjacent to the outer surface of the part that was free orsubstantially free of cells (“solid”). Part C was less dense than PartD.

Example 3

In Example 3, block parts were molded using the MFIM process at variousdecompression volumes (Trial A) and various decompression volumes anddecompression times (Trial B).

TABLES 8-10 show the material composition, mold geometry information,and processing settings used for Trials A and B.

TABLE 8 Material Composition Weight % Polymer: LDPE 82% Filler: Talc 15%Foaming agent: Hydrocerol ® BIH 70  3%

TABLE 9 Baseline Mold Parameters Block Mold (2 × 2 × 2 inch) ASTM Mold(5.08 × 5.08 × 5.08 cm) Mold Cavity Volume (cc) 132.74 Sprue Volume (cc) 17.39 Total Volume (cc) 150.13

Composite LDPE/talc pellets were mixed with foaming agent just prior tomolding.

Trial A

In Trial A, all variables were held constant except the volume ratio ofpolymer to decompression volume (empty space) in the barrel prior toinjection. The settings for each sample run of Trial A are shown inTABLE 10:

TABLE 10 Settings for Trial A Sample Sample Sample Sample Sample 1 2 3 45 Barrel 171|185| 171|185| 171|185| 171|185| 171|185| Temperatures (°C.) 177|166 177|166 177|166 177|166 177|166 Mold 21 21 21 21 21Temperature (° C.) Injection 4137 4137 4137 4137 4137 Pressure (kPa)Back pressure (psi) 0 0 0 0 0 Decompression volume 0 7.7 15.4 23.2 30.1(cc) Screw Speed (rpm) 165 165 165 165 165 Overall 76.5 76.5 76.5 76.576.5 cycle time (sec) Shot Size (cc) 92.62 84.91 77.19 69.47 61.75Decompression time (sec) 20 20 20 20 20

The volume of molten foam injected into the polymer cavity was constant,but the density of the molten foam was a function of the polymershot/decompression volume ratio. The polymer shot/decompression volumeswere varied giving parts with weight and density as shown in TABLE 11:

TABLE 11 Trial A Part Weights and Densities Polymer Shot Total as aPercentage Molten of Total Polymer Foam Volume Volume Decompression Shot(Polymer + Decompression Part Part in Barrel Volume in VolumeDecompression time Weight Density Sample (cc) Barrel (cc) (cc) Volume)(sec) (g) (g/cc) 1 92 0 92 100%  20 94.1 0.71 2 85 7 92 92% 20 90.4 0.683 77 15 92 83% 20 86.0 0.65 4 69 23 92 75% 20 81.8 0.62 5 62 30 92 67%20 76.1 0.58

The results in TABLE 11 indicate that by decreasing the mass and volumeof polymer in the molten foam shot with a commensurate increases indecompression volume, the density of the resultant part can be varied.

Trial B

In Trial B, five moldings under the same conditions as Trial A wereconducted three times; once with a decompression time 20 seconds (sameas Trial A), once with a decompression time of 70 seconds, and once adecompression time of 120 seconds. The 15 resultant foam-molded partswere weighed and the density calculated using the volume of the moldcavity. The part density was plotted as a function of decompressionvolume for each of the three decompression times. The plots are shown inFIG. 5. As seen in FIG. 5, part density varied as a function ofdecompression volume. Further, as shown in FIG. 5, the greater thedecompression time, the denser the part.

Example 4

In Example 4, two series of trials were run using the MFIM process,Series I and Series II. In Series I, a constant injection speed was usedbut mold close height was varied. In Series II, mold close height wasincreased with increasing injection speed. In Series II, all conditionswere kept constant except injection speed (cc/sec) and mold closeheight. In the trials, LDPE/talc pellets were dry blended with thefoaming agent and mixed during loading into the molding machine.

TABLES 12-13 below show the material composition of the injected blendand the base mold configuration used for the trials.

TABLE 12 Material Composition Weight % Polymer: LDPE 82% Filler: Talc15% Foaming agent: Hydrocerol ® BIH 70  3%

TABLE 13 Baseline Mold Parameters Block Mold (2 × 4 × 4 inch) ASTM Mold(5.08 × 10.16 × 10.16 cm) Mold cavity volume (cc) 524.39 Sprue Volume(cc)  17.39 Total Volume (cc) 541.78

Series I

In Series I, an injection velocity of 394 cubic centimeters per secondwas used, and three trials were run, Trial A with a mold close height of1.02 mm producing Part A; Trial B with a mold close height of 0.76 mmproducing Part B, and Trial C with a mold close height of 0.51 mmproducing Part C. The settings for the Series I trials are shown inTABLE 14:

TABLE 14 Settings Barrel Temperatures (° C.) 154|185|177|166 MoldTemperature (° C.) 20 Injection Speed (cc/sec) 394 Back pressure (psi) 0Screw Speed (rpm) 165 Screw Rotate Delay Time (sec) 100 Hold Pressure(kPa) 0 Hold Time (sec) 10 Fill Time (sec) 1.78 Mold Close Height (mm)1.02, 0.76, 0.51

During each molding cycle (each of Trial A, Trial B, and Trial C), astrain gauge (Kistler Surface Strain Sensor Type 9232A, available fromKistler Holding AG. Winterthur, Switzerland) was mounted just above orinside the molding cavity. The strain sensor contained two piezoelectricsensors that measured the strain of the aluminum cavity as a function oftime during the molding cycle. The strain measurement was used as anindirect measure of the force acting on the surface of the mold cavityresulting from the injection of molten foam and any subsequentadditional foaming that occurred within the mold cavity. The cavitystrain measurements are shown in FIG. 6 for Trial A, 1.02 mm gap height(line A); Trial B, 0.76 mm mold close height (line B); and Trial C, 0.51mm mold close height (line C). In FIG. 6 the strain (unit extension perunit length) is plotted versus time in seconds. The strain curvesindicate that the pressure was higher in Trial C than in Trial B andTrial B was higher than in Trial A.

FIG. 7 includes photographic images showing a side view, a top view, anoblique view, and a bottom view of Parts A, B, and C. Parts A and Bshowed evidence of collapse, as the parts did not sufficiently match themold cavity shape. Part A showed more collapse than Part B. Part C wasmore fully formed than either of Parts A and B in that the edges of PartC were better defined, and Part C conformed better to the mold cavityshape, and the interior of the part appeared more homogenous.

It was believed that parts could partially collapse in the cavity duringmolding if sufficient pressure is not supplied to stabilize the foam inthe cavity during solidification. Accordingly, in Series II the mold wasclosed more tightly at slower injection rates in order to maintainsufficient pressure to prevent collapse of the part during molding.

Series II

In Series II the gap between mold halves, the mold close height, wassystematically decreased as the injection rate was decreased. Themolding conditions used were the same as those in Series I except thatthe injection rates and mold close heights used were those as shown inTABLE 15:

TABLE 15 Series II Trial Injection Rate (cc/sec) Mold Close Height (mm)A′ 394 +0.51 (gap) B′ 317 +0.21 (gap) C′ 162 −0.26 (pressure) D′  85−0.51 (pressure)

Four parts were produced in Trials A′, B′, C′, and D′, Parts A′, B′, C′,and D′ respectively.

Each of Parts A′, B′ C′ and D′ was cut into two, and the cross sectionphotographed. The photographic images are shown in FIG. 8. In order toproduce a part that did not collapse before solidification, the moldhalves had to be increasingly closed, as shown in TABLE 15, until theywere actually being pressed together (as indicated by negativedimension).

Parts A′, B′ C′, and D′ showed no evidence of collapse, had well definededges and surfaces, and appeared fairly uniform. Accordingly, parts weremade using the MFIM process using drastically different injection ratesby controlling the pressure within the cavity during injection, e.g. byvarying mold close height.

Example 5

In Example 5, the same LDPE composite material as Examples 1-3 was usedin a non-standard two cavity mold with molding parameters as shown inTABLES 16-18.

TABLE 16 Material Composition Weight % Polymer: LDPE 82% Filler: Talc15% Foaming agent: Hydrocerol ® BIH 70  3% LDPE/Talc pellets dry blendedwith foaming agent and mixed during loading into molding machine.

TABLE 17 Baseline Mold Parameters Total Mold Cavity Volume (cc) 1232Sprue & Runner Volume (cc) 18 Single Mold Cavity Volume (cc) 607

TABLE 18 Machine Setpoints and Mold Details Shot size (cc) 555.7Decompression volume (cc) 463.1 Decompression time (s) 160 Pack VolumeTime (sec) 0.00 Pack Volume Speed (cm/sec) 0.00 Hold Press (kPa) 0.00Hold Time (sec) 10.00 Back Pressure (kPa) 0.00 Cushion (cm) 0.00 CoolingTime (sec) 180.00 Sprue Break (cm) 2.54 (Stack) Sprue Volume (cc) 18Barrel Temperatures (° C.) 163|185|177|166 Mold Temperature (° C.) 26.7Injection Velocity (cc/sec) 394 Screw Speed (rpm) 165 Screw Rotate DelayTime (sec) 20 Fill Time (sec) 2.385

Example 5 produced the parts 51 shown in FIG. 9. During injection themolten foam melt entered through the sprue 52 and split off into twoseparate channels to fill the parts 51 substantially simultaneously.Accordingly, the MFIM process could be used to form parts by splittingthe melt into multiple pathways in the mold.

Example 6

A first part was molded using a formulation of 15 wt. % talc/85 wt. %polycarbonate composite was blended with 3 wt. % Hydrocerol® XH-901prior to loading into the injection molding machine. The first part wasformed using the MFIM process. Process details are provided in TABLES 19and 20. The part was made using a 4×2×2 block mold (5.08×10.16×10.16 cm)with a mold cavity volume of 524.4 cc and a sprue volume of 17.4 cc. Thesprue was cut from the part, and the part was then subject to X-raytomography to quantify the cellular structure formed within the5.08×10.16×10.16 cm geometry.

TABLE 19 Material Composition Weight % Polymer: Polycarbonate 82%Filler: Talc 15% Foaming Agent: Hydrocerol ® XH-  3% 901

TABLE 20 Settings Barrel Temperatures (° C.) 288|282|277|260|232|204Nozzle Temperature (° C.) 288 Feed Throat Temperature (° C.) 65.5 MoldTemperature (° C.) 32 Injection Speed (cc/s) 655.48 Specific BackPressure (kPa) 6,895 Polymer Shot Size (cc) 139 Decompression Size (cc)90 Total Molten Foam Shot Size (cc) 229 Screw Speed (cm/sec) 7.62 ScrewRotate Delay Time (sec) 40 Appx. Decompression Time (sec) 80 HoldPressure (kPa) 0 Hold Time (sec) 0 Cooling Time (sec) 120 Clamp Force(kN) 267

X-Ray tomography was carried out using a Zeiss Metrotom 800 130 kVImaging system (available from Carl Zeiss AG of Oberkochen, Germany).The instrument measured the attenuation of the X-ray radiation due tothe component geometry and the density of the material used. The columndata were calculated using the Feldkamp reconstruction algorithm, astandard technique for the industry. The instrument had a flat paneldetector of 1536×1920 pixels for an ultimate resolution of 3.5 μm underthe conditions of this measurement.

An isometric image of a full Zeiss 3D Tomography scan of the first partis shown in FIG. 10, with the solid polymer fraction shown astransparent, the cells shaded for visualization, and the cutting planeA-A for single cross-section indicated. FIG. 11 is a single-plane crosssection A-A selected from the X-ray data with a threshold analysisapplied to allow for discrete cell identification and subsequentquantitative analysis.

The circularity of the cross-sections of the cells was obtained. Thecircularity of these cross sections was used as a measure of thesphericity of the cells. Accordingly, circularity and sphericity areused interchangeably in the Examples. Quantitative analysis shown inFIG. 12 revealed a cell distribution of both counts and average size asa function of the circularity of each cell. A circularity value of zerorepresents a completely non-spherical cell, and a value of 1 representsa perfectly spherical cell. The data showed a distribution of cell sizesand shapes. With the exception of the most deformed cells (indicated by0.1-0.2 on the circularity scale), there was an inverse relationshipbetween the average cell size and the number of cells of a givencircularity. Further, there is an inverse relationship between theaverage cell size and the number of cells.

Using an MFIM process, a second, spherical, part of diameter of sixinches (15.24 cm) was molded from low-density polyethylene (LDPE) usingthe polymer formulation and processing parameters as outlined in TABLE21 and TABLE 22. The LDPE/talc pellets were dry blended with the foamingagent, Hydrocerol® BIH 70 and mixed during loading into the moldingmachine.

TABLE 21 Material Composition Weight % Polymer: LDPE 82% Filler Talc 15%Foaming Agent: Hydrocerol BIH-70  3%

TABLE 22 Settings Barrel Temperatures (° C.) 182|174|171|171|166|135Nozzle Temperature (° C.) 182 Feed Throat Temperature (° C.) 54 MoldTemperature (° C.) 21 Injection Speed (cc/sec) 655.5 Specific BackPressure (kPa) 6895 Polymer Shot Size (cc) 574 Decompression Size (cc)1475 Total Molten Foam Shot Size (cc) 2048 Screw Speed (cm/sec) 15.24Screw Rotate Delay Time (sec) 60 Appx. Decompression Time (sec) 100 HoldPressure (kPa) 0 Hold Time (sec) 0 Cooling Time (sec) 160 Clamp Force(kN) 178

FIG. 13 is an x-ray tomographic image of a cross section of the sphere.As seen in FIG. 13, the outer region contained a plethora of smallercell sizes with larger cells in the central region.

FIG. 14 shows a plot of average cell size and average cell count versusaverage cell circularity and reveals an inverse relationship between theaverage cell size and the circularity and an inverse relationshipbetween the average cell size and the number of cells.

Example 7

An MFIM process was used to mold an LDPE composite sphere (92 wt. %polymer, 5 wt. % talc, and 3 wt. % Hydrocerol® BIH 70) with a diameterof three inches (7.62 cm) and the resulting foam cell structure detailedin FIGS. 15-18. Molding conditions are provided in TABLE 23. The partwas molded on an Engel Victory 340 Ton injection molding press in acustom designed, water cooled aluminum mold. The volume of the moldcavity was 15.38 in³ (252 cc), the shot size was 5 in³ (82 cc), and thedecompression volume in the barrel was 5 in³ (82 cc). The decompressiontime was 77 seconds. The molded part weight was 80.31 g, yielding afinal part density of 0.32 g/cc.

TABLE 23 Machine Setpoints and Mold Details Pack Volume Time (sec) 0.00Pack Volume Speed (cm/sec) 0.00 Hold Press (kPa) 0.00 Hold Time (sec)0.00 Cushion (cm) 0.00 Cooling Time (sec) 120.00 Sprue Break (cm) 2.54(Stack) Sprue Volume (cc) 18 Mold Cavity Volume (cc) 252 BarrelTemperatures (° C.) 180|174|166|160 Mold Temperature (° C.) 13 InjectionSpeed (cm/sec) 51 Back Pressure (kPa) 689.5 Screw Speed (cm/sec) 30.5Screw Rotate Delay Time (sec) 40 Fill Time (sec) 2.38 Clamp Force (kN)98

After removal from the mold, the part was aged in ambient conditions for24 hours, then scored and submerged in liquid nitrogen for two minutes.After removal from the liquid nitrogen, the sphere was fractured alongthe scored surface line and the fracture surface was imaged using anenvironmental scanning electron microscope (ESEM) (FEI Quanta FEG 650).The images shown in FIGS. 15-18 are micrographs at variousmagnifications taken of the fracture surface of the sphere part using alarge field detector, 5.0 kV and 40 Pa of pressure.

The white box in FIG. 15 indicates the area detailed in FIG. 16. Thewhite box in FIG. 16 indicates the area detailed in FIG. 17.

In FIG. 17, the cells to the left of the image are larger and relativelyspherical, whereas those cells to the right side of the photographappear progressively flattened as they approach the surface of thesphere.

The image in FIG. 18 details the area indicated by the white box in FIG.17. As seen in FIG. 18, there is a gradual transition from spherical to“flattened” or compressed cells moving towards the surface of the part.

Example 8

To establish the baseline differences between parts of standardthickness manufactured under standard foam molding conditions, arecently published study of standard foam injection molding(Paultkiewicz et al., Cellular Polymers 39, 3-30 (2020)) was used toestablish a molding parameter baseline using a 16-run statisticalanalysis designed experimental (DOE) approach. Material (standardmolding grade polypropylene with 0 wt %, 10 wt %, and 20 wt. % talc; and0 wt %, 1 wt %, and 2 wt % of Hydrocerol® BIH 70 (foaming agent)) wascompounded to specifications outlined in the publication in order toclosely mimic the baseline study. The study was designed to investigatethe influence of foaming agent concentration, talc content, and processconditions on selected properties of injection molded foam parts. Astandard ISO tensile bar mold having cavity dimensions of 4.1 mm inthickness, 10 mm width in the gauge length, and 170 mm in length wasused. No special venting was developed for the ISO bar mold. Afterensuring that the injection molding machine, material formulations, andprocess window were able to replicate results published by Paultkiewiczet al., a second study was carried out using process variables specificto MFIM, specifically decompression volume and decompression time, whilepressure and holding time (important variables in the published study)were set to a constant value of zero kN and zero seconds respectively.

The molding was completed using an Engel Victory 340 Ton machineequipped with water cooling. The constant and variable processconditions that were used are shown in TABLE 24 for both the “standard”foam molding process and the MFIM molding process.

TABLE 24 Constant Machine Setpoints and Mold Details Standard MoldingMFIM Molding Variable Settings Designed Experiment Variable Low/Med/Highlevels Foaming agent content (ba) (wt 0/1/2 0/1/2 %) Talc content (ta)(wt %) 0/10/20 0/10/20 Injection Velocity (cc/sec) 34.4/54.6/74.634.4/54.6/74.6 Hold Pressure (kPa) 75840/19995 0 Hold time (sec) 2/20 0Decompression Volume (cc) — 0/7.4/14.7 Decompression Time (sec) — 15Constant Settings Cooling Time (sec) 20 Mold Temp (° C.) 20 InjectionTemp (° C.) 210 Specific Backpressure (kPa) 6895 Cooling Time (sec)20.00 Barrel Temperatures (° C.) 210/210/210/177/163/149/38 Shot size(in³) 44.2 29.5

The designed study required 16 combinations of processingconditions/polymer formulation (16 runs) for each of the standardmolding and MFIM molding studies. Multiple replicates were conducted ofeach run, producing replicate parts for each run. TABLE 25 outlines thevariation between runs in both the standard and MFIM designed runs. Theruns were conducted in a random order to avoid bias. The L/T ratio forthe ISO tensile bar is 40.5.

TABLE 25 Molten Foam Injection Molding Standard Foam Molding ProcessProcess Decom- Foaming Talc Hold Foaming Talc Run pression agent loadingRun pressure agent loading # volume (cc) (%) (wt %) # (kPa) (%) (wt %) 10 0 0 1 75842 0 0 2 14.7 0 0 2 75842 0 0 3 0 0 20 3 75842 0 20 4 14.7 020 4 75842 0 20 5 7.4 0 10 5 75842 0 10 6 7.4 1 0 6 19995 1 0 7 7.4 1 207 19995 1 20 8 0 1 10 8 19995 1 10 9 14.7 1 10 9 19995 1 10 10 7.4 1 1010 19995 1 10 11 7.4 1 10 11 19995 1 10 12 0 2 0 12 19995 2 0 13 14.7 20 13 19995 2 0 14 0 2 20 14 19995 2 20 15 14.7 2 20 15 19995 2 20 16 7.42 20 16 19995 2 10

After molding 32 unique process combinations of the two 16-run DOEstudies, five samples of each series were mechanically tested fortensile strength and the fracture surface imaged after fracture. Arepresentative selection of ISO bar cross sections from Runs 10, 11, 14,and 15 of the standard foam molding process are shown in FIG. 19 and arepresentative selection of ISO bar cross-sections from Runs 9, 10, 15,and 16 of the MFIM process are shown in FIG. 20.

Differences between the standard foam molding technique as adopted fromrecent literature and the MFIM process are apparent when examining thecross-section images. The structure in the standard process bars consistof relatively few, but well defined, spherical cells flanked on allsides by a thick region of polymer lacking cells. The cross-sectionimages obtained from the standard foam molding process are in goodagreement with those in the publication by Paultkiewicz et al. and arerepresentative of the current industry standard. In contrast, thetypical cross sections of the MFIM molded ISO bars display a cellstructure with more asymmetric, deformed cells.

The cells in the MFIM cross-section also proceed to the region adjacentto the surface in almost all cases, similar to previous examplesdescribed herein, and despite being a much thinner part with a muchlarger L/T ratio (40.5) than previously described. The results clearlyindicate that the adoption of the decompression step in MFIM, incombination with eliminating the standard foam molding process variablesof hold pressure and time, results in a significantly different cellstructure in molded parts.

Tensile tests of five replicate parts from MFIM Run 9 were run. FIG. 21shows a representative cross section and a series of stress/strain plotsfor the five parts tested from MFIM Run 9.

Tensile tests of five replicate parts from Run 10 made using thestandard foam molding process were run. FIG. 22 shows a representativecross section and a series of stress/strain plots for the five partstested from standard foam process Run 10.

The average tensile strength of the five parts from MFIM Run 9 was lessthan that of the average of the five parts from standard foam moldingprocess Run 10. However, the MFIM parts showed a greater strain(elongation) at break.

More cells were visible in the cross section of the MFIM part from Run 9(102 cells) than in the standard foam molding process part from Run 10(19 cells).

X-ray tomography scans (completed under conditions described in Example5) were completed for a randomly selected replicate part from Run 15 ofthe standard foam molding process (shown in FIG. 23) and for a randomlyselected replicate part produced during Run 9 of the MFIM process (shownin FIG. 24). Both FIG. 23 and FIG. 24 show a “top” view, taken at 50%depth and a “side” view, also taken at 50% depth.

In the developed cell structure of the standard foam molding process ISObar (FIG. 23), cells were circular in shape and the regions adjacent tothe surface of the bar lacked cells.

In contrast, the ISO bar produced via the MFIM process as shown in FIG.24 includes a high population of elongated cells and cells are found inthe region adjacent to the surface of the part.

Example 9

To explore the dependence of final cell structure on MFIM processingconditions, eight tensile bars of LDPE were molded using the MFIMprocess on an Engel Victory 340 Ton injection molding machine. The moldincluded an aluminum material modified tensile bar cavity havingdimensions of 24 cm in length, a thickness of 2.54 cm, and a variablewidth with gauge length of 6 cm and a gauge width of 2.54 cm tapering toflanges of 3.5 cm in width. The large tensile bar was fed from a coldsprue and runner system through a gate 1.0 cm in diameter. The materialformulations consisted of LDPE with or without talc, always containing 2wt % foaming agent Clariant Hydrocerol® BIH 70. The melt temperature wasset to the profile detailed in TABLE 26, and residence time in thebarrel was 13 minutes before building a shot for injection. Afterbuilding the shot, the screw was retracted to give a decompressionvolume of either 4.0 cubic inches (66 cc) or 6.0 cubic inches (98 cc)and the LDPE foaming agent mixture was allowed to foam for either 15 or45 seconds into the empty barrel space prior to injection. The study wascompleted for both unfilled LDPE and 15% talc filled LDPE. Detailedprocess conditions are shown in TABLE 26.

TABLE 26 Constant Machine Setpoints and Mold Details for MFIM of LargeTest Bar Designed Experiment Variable Low/High levels Talc Content (wt%) 0/15 Decompression Volume (dv) (cc) 66/98 Decompression Time (dt)(sec) 15/45 Constant Settings Foaming Agent Content (wt %) 2 CoolingTime (sec) 60 Mold Temp (° C.) 10 Injection Temp (° C.) 182 InjectionVelocity (cc/sec) 328 Specific Back Pressure (kPa) 6895 Cooling Time(sec) 60.0 Barrel Temperatures (° C.) 210/210/210/177/163/149/38 ShotSize (cc) 98 Clamp Force (kN) 89

FIG. 25 shows an X-ray scan of one of the parts from this study, showingthe overall shape of each part.

FIG. 26 depicts a cross section of each test bar molded in the study,cut from the middle of the gauge length, with the variable parametersindicated. The sample set includes two primary groups: samples made withtalc and samples made without talc. In FIG. 26, the sample set on theleft depicts those parts made without talc. These parts display asmaller cell structure in the core of the part, and the integrity of thedeveloped cell structure is largely unaffected by the changes indecompression ratio and decompression time, indicating the decompressionratios and times were all within an acceptable range.

The sample set on the right depicts those bars containing 15 wt % talc.Some smearing on the part surfaces resulted from knife damage on thelow-modulus LDPE and is not representative of part quality. The cellstructure in the talc parts was consistently larger, and the circularityof the cells was slightly lower than the talc-free equivalents.

An X-ray tomography image was taken of a cross section from the majorsurface about 50% into the MFIM part made with 15% talc, 6 in³ (98 cc)decompression volume, and 15 seconds decompression time. The image isshown in FIG. 27.

Example 10

A tensile bar part was made using a standard foam molding process fromLDPE loaded with 15 wt % talc, and 2 wt % Hydrocerol® BIH 70 usingprocessing parameters as described for Example 9, but without thedecompression step of the MFIM process. This standard foam molding partwas compared with the MFIM part made with 15% talc, 6 in³ (98 cc)decompression volume, and 15 seconds decompression time from Example 9.Using methods as described in Example 6, X-ray tomography images weretaken of a central portion of each of the parts (MFIM molding andstandard foam molding) at a variety of depths from a major surface.Cross section images were also recorded. The images are shown in FIG.28.

X-ray tomographic analysis of cell count, cell circularity, and averagecell size (longest dimension of cell) was performed on the images ofeach tensile bar part (MFIM and standard process materials) at eachdepth from the major surface. Cell count, cell circularity, and averagecell size were each plotted against depth of the cross section; and therespective plots are shown in FIGS. 29-31 respectively.

As shown in FIG. 29, cell count was higher in the MFIM molded part atall depths. As seen throughout the Examples and Figures, the part moldedusing the standard foam molding process appears to have no orsubstantially no cells in the region or “skin” adjacent to the surface,e.g. in about the first 2.5 mm of depth from the major surface, whereascells are present in the part molded using the MFIM process within theregion between about 2.5 mm below the surface and the surface.

As shown in FIG. 30, in general cell circularity was greater in thestandard foam molding process sample than in the MFIM-molded part excepttowards the middle of the MFIM part, where circularity was also high inthe MFIM molded sample.

As shown in FIG. 31, cell size was generally larger for the standardfoam molded tensile bar part, but fell off rapidly to zero in theregions proximal the outer surfaces (e.g. within 2.5 mm of the surface).In contrast, cell size was more uniform through the depth of theMFIM-molded part, and cells continued right to the surface.

The same trends are seen by visual examination of the cross sectionsshown in FIG. 28. Within 2.5 mm of any outer surface, the standard foammolded part appears to lack cells, whereas cells are visible up to theouter surface in the MFIM part.

Example 11

A large sample of recovered ocean plastic was analyzed usingdifferential scanning calorimetry and was estimated to consist ofapproximately 85 wt % of HDPE, with the balance comprising polypropyleneand contaminants.

Two parts were successfully molded from the ocean plastic using an MFIMprocess, a 4″×4″×2″ brick and a sphere of 15.24 cm diameter. Molding wasconducted using an Engel Duo 550 Ton injection molding machine(available from Engel Machinery Inc. of York, Pa., USA). Both parts werecenter-gated and filled by a viscous coil-folding flow.

Processing parameters and characteristics of the resulting part arelisted in TABLE 27 and TABLE 28 respectively:

TABLE 27 6″ Sphere 4″ × 4″ × 2″ Brick Material Ocean Plastic OceanPlastic Machine Engel Duo 550 Ton Engel Duo 550 Ton Decompression volume(cc) 819 295 Decompression time (sec) 340 60 Foaming agent BIH 70 (wt %)3 3 Cooling Time (sec) 400 120 Mold Temp (° C.) 35 38 Injection Temp (°C.) 204 204 Injection Velocity (cc/sec) 655 787 Specific Back Pressure(kPa) 6895 13790 Barrel Temperatures (° C.) 204/191/177/163/149/107/54Shot size (cc) 1229 279 Clamp Force (kN) 445 445 Hold Time (s) 0 0 HoldPressure (kPa) 0 0

TABLE 28 Part Characteristics 6″ Sphere Brick Part Weight (g) 921.6253.2 Volume (without runner) (cc) 1856 524.3 Part Density (g/cc) 0.4960.482

Example 12

A sphere of nine inches (22.86 cm) in diameter, “Sample 10”, was moldedusing the MFIM process described herein. Further, a second sphere ofnine inches (22.86 cm) in diameter, Sample 20, was molded using avariant process. The variant process, termed herein “reverse MFIM”process was as follows:

A) A mixture was prepared by blending a polymer (which may be in theform of pellets, powder, beads, granules, and the like) with a chemicalfoaming agent, and any other additives such as a filler. The mixture wasintroduced to the injection unit, and the rotating injection unit screwmoved the material forward in the injection molding machine barrel, thusforming a heated fluid material in accordance with normal injectionmolding processes. B) The screw was moved backwards towards the hopper,creating an intentional space between the screw and the nozzle withinthe barrel. C) A set volume of the material was dosed to the front ofthe barrel of the injection unit by rotation of the screw, thus movingthe set volume from the feed zone to the front of the screw and into theintentional space created in step B. During this feed step, the screwwas rotated to move melted material to the space in the barrel betweenthe screw and the nozzle, thereby providing the set volume. However, theset volume occupied only part of the intentional space, therebyproviding volume for the shot to foam and expand, the decompressionvolume. D) The material sat in the barrel between the screw and thenozzle for a period of time, termed herein the “decompression time”.During the decompression time, the material expanded due to foaming tofill or partially fill the space created in step (B). E) The molten foamwas injected into the mold cavity by forward translation of the screwand/or rotation of the screw.

Thus the regular and reverse MFIM processes differed from each other inthat in the MFIM process, the screw was rotated to introduce the shot tothe front of the barrel before the screw was translated backwards toallow for a decompression space; whereas in the reverse process thescrew was translated backwards to allow for a decompression space beforethe screw was rotated to introduce the shot of material into theintentionally created space.

Sample 10 and Sample 20 were both molded of virgin LDPE containing 2%Hydrocerol® BIH 70, 2% talc, and 1% yellow colorant. Molding was carriedout on the Engel Duo 550 Ton injection molding machine (available fromEngel Machinery Inc. of York, Pa., USA). The mold was a spherical cavitywithin an aluminum mold fed by a cold runner and sprue.

The processing parameters are shown in TABLE 29:

TABLE 29 Sample 10 Sample 20 Process Method MFIM Reverse MFIM Shot Size(cc) 1639 1762 Decompression Volume (cc) 1475 1475 Batter (cc) 3114 3236Shot to Decompression Volume 10:9 10:9 Ratio Cooling Time (sec) 300 300Screw Rotation Delay Time (sec) 140 140 Metering Performance (cc/sec)32.8 32.8 Decompression Speed (cc/sec) 164 164 Approximate DecompressionTime 101 106 (sec) Clamp Force (kN) 89 89 Specific Back Pressure (kPa)6895 6895 Injection Pressure (kPa) 52476 53827 Injection Speed (cc/sec)655 655 Screw Speed (cm/sec) 15.24 15.25 Mold Temperature (° C.) 10 10Shot Weight (g) 1334 1335

The density of the parts, both Sample 10 and Sample 20, was 0.214 g/ccwith a density reduction in both cases of 77%.

A photograph of Sample 20 is shown in FIG. 32 and of Sample 10 in FIG.33, with each spherical part mounted on a stand. As can be seen in theFigures, Sample 20 made using the “reverse MFIM process” exhibited anuneven surface, whereas the surface of Sample 10 made using the MFIMprocess was much more even. Average wrinkle depth was estimated usingoptical microscopy and X-ray tomography. The average wrinkle depth wasmeasured at less than 50 microns for Sample 10, but 565 microns forSample 20.

Each of Sample 10 and Sample 20 was cut into half to provide a crosssection at the maximum diameter. The cross section of the four pieceswas photographed. One half of Sample 20 made by the reverse MFIM methodis shown in shown in FIG. 34 and one half of Sample 10 is shown in FIG.35. Close examination of the edge showed that in Sample 10 and Sample20, cells were found right up to the surface, e.g. within 2.5 mm of thesurface, unlike parts produced elsewhere in the Examples by the standardfoam method.

X-ray tomography was performed on the first inch of depth of a sample ofSample 10 and of Sample 20, and using methods described for Example 6,cell count and cell size was measured for different distances from thesurface of each sample. Plots are given in FIGS. 36 and 37, wherein“MFIM” refers to Sample 10 and “Reverse MFIM” refers to Sample 20.

Two further sphere parts, Parts 6 and 7, were prepared under the sameconditions and with the same polymer/talc/colorant/foaming agent mix asSample 10, i.e. by the MFIM method. Five cuboid parts, eachapproximately 2 inches by 2 inches by 1 inch, were cut from each ofParts 6 and 7, and compression modulus (stress versus strain) wastested. The average stress versus the average strain (MFIM method) wasplotted and is shown in FIG. 38.

Two further sphere parts, Parts 22 and 24, were prepared under the sameconditions and with the same polymer/talc/colorant/foaming agent mix asSample 20. Five cuboid parts, each approximately 2 inches by 2 inches by1 inch (about 5.1 cm by 5.1 cm by 5.1 cm), were cut from each of Parts22 and 24, and compression modulus (stress versus strain) was tested.The average stress versus the average strain (reverse MFIM method) wasplotted and is also shown in FIG. 38. as seen in FIG. 38, thecompression moduli of the parts made by the MFIM process (average ofParts 6 and 7) and the parts made by the reverse MFIM process (averageof Parts 22 and 24) are similar.

Five strips were cut from each of Parts 6 and 7 (MFIM) and 22 and 24(reverse MFIM). Each strip was approximately 1 inch by 1 inch by 8inches. The flexural modulus (stress versus strain) was tested for allof the strips, and the results averaged for the ten MFIM-produced stripsand the results averaged for the ten reverse MFIM strips. The resultsare plotted in FIG. 39.

Example 13

Parts were fabricated using MFIM methods as described herein, of variousshapes and materials as shown in TABLE 30. The parts were crosssectioned. In all cases, a region proximal the surfaces included cellsof lower size, but moving away from a surface, cell size increased. Theregion of reduced cell size closer to the surfaces transitioned to alarger cell size further from the surface. While the transition wasgradual and so there was no a distinct layer of smaller size and adistinct layer of larger size, using microscopy the relative areas ofthe region of smaller or “compressed” cells and the region of largercells was estimated by eye and confirmed by light microscopy, and isshown in TABLE 30. While the numbers are only estimates, examination ofthe images showed that the depth of the region and the percent area thatwas occupied by “compressed” cells varied widely, perhaps depending onpart shape, material, and/or run conditions.

TABLE 30 Estimated Sphere Estimated Percent of diameter Percent ofCompressed Material Filler (inches) Core Zone LDPE — 3 in Sphere 91%  9%LDPE 15% Talc 3 in Sphere 80% 20% Nylon 6 15% Talc 3 in Sphere 85% 15%LDPE 15% Talc 6 in Sphere 87% 13% LDPE — 6 in Sphere 85% 15% High-Impact15% Talc 6 in Sphere 85% 15% Polystyrene Estimated Estimated Percent ofGeometry Percent of Compressed Material Filler (inches) Core ZoneMetallocene — 4 × 4 × 2 66% 34% Polyethylene High-Impact 15% Talc 4 × 4× 2 53% 47% Polystyrene ABS 20% Talc 4 × 4 × 2 71% 29% EstimatedEstimated Percent of Percent of Compressed Material Filler Geometry CoreZone LDPE — Large Tensile 54% 46% Bar LDPE 15% Talc Large Tensile 73%27% Bar Estimated Estimated Percent of Percent of Compressed MaterialFiller Geometry Core Zone Polypropylene 10% Talc ISO Tensile Bar 65% 35%

Example 14

A first part was molded using a formulation of 98 wt. % metallocenepolyethylene was blended with 2 wt. % Hydrocerol® BIH 70 prior toloading into the injection molding machine. The first part was formedusing the MFIM process. Process details are provided in TABLE 31 andTABLE 32. The part was made using a 2″×4″×4″ block mold(5.08×10.16×10.16 cm) with a mold cavity volume of 524.4 cc and a spruevolume of 17.4 cc. The sprue was cut from the part, and the part wasthen subject to compression load testing to quantify the compressivestrength properties of the cellular structure formed within the 2″×4″×4″geometry.

TABLE 31 Material Composition Weight % Polymer: Metallocene Polyethylene98% Foaming Agent: Hydrocerol BIH 70  2%

TABLE 32 Settings Barrel Temperatures (° C.) 204 | 193| 188 | 188 | 177| 166 | 166 | Nozzle Temperature (° C.) 204 Feed Throat Temperature 49(° C.) Mold Temperature (° C.) 55 Injection Speed (cc/s) 655.48 SpecificBack Pressure (kPa) 10,342 Polymer Shot Size (cc) 245.8 / 327.7 / 409.7Decompression Size (cc) (for 360.5 / 163.9 / 81.9 samples A/B/C) ScrewSpeed (cm/sec) 7.62 Screw Rotate Delay Time (sec) 100 / 740 / 740 Appx.Decompression 60 Time (sec) Hold Pressure (kPa) 0

Compression testing was carried out on an Instron Universal TestingSystem (available from Instron USA, Norwood, Mass., USA). Each moldedfoam block was placed between the testing platens and stabilized withinan environmental chamber at 30° C. for five minutes prior to testing.The instrument was equipped with a 250 kN load cell. The compressiontest rate was 5 mm/min.

Results showed a compressive modulus was 19 MPa for sample A (0.37g/cc), 39 MPa for sample B (0.45 g/cc) and 55 MPa for sample C (0.57g/cc). As shown in FIG. 40, the compressive strength of metallocenepolyethylene (mPE) blocks increases with increasing density.

What is claimed is:
 1. A method of forming a polymer foam article, themethod comprising: heating and mixing a thermoplastic polymer with apneumatogen source to form a molten pneumatic mixture, wherein thetemperature of the molten pneumatic mixture exceeds the temperature atwhich the pneumatogen source produces a pneumatogen at atmosphericpressure, and wherein a pressure applied to the molten pneumatic mixtureis sufficient to substantially prevent formation of pneumatoceles;collecting a selected amount of the molten pneumatic mixture in acollection region; defining an expansion volume in the collection regionproximal to the molten pneumatic mixture to form a molten polymer foamfrom the molten pneumatic mixture; dispensing the molten polymer foamfrom the collection region into a cavity defined by a mold, wherein themolten polymer foam contacts the surface of the mold defining thecavity; and cooling the molten polymer foam in the mold cavity to form asolidified polymer foam article.
 2. The method of claim 1 wherein thedispensing comprises partially filling the mold cavity.
 3. The method ofclaim 1 wherein the dispensing comprises substantially filling the moldcavity.
 4. The method of claim 1 wherein the dispensing comprisescompletely filling the mold cavity.
 5. The method of claim 1 wherein themold cavity comprises a volume of more than 1000 cm³.
 6. The method ofclaim 1 wherein the mold cavity comprises a volume of more than 5000cm³.
 7. The method of claim 1 wherein the mold cavity comprises a volumeof more than 10,000 cm³.
 8. The method of claim 1 wherein the moldcavity comprises a volume of more than 50,000 cm³.
 9. The method ofclaim 1 wherein the mold cavity comprises a distance of 2 cm or morebetween two points on the surface of the mold defining the cavity. 10.The method of claim 1 wherein the mold cavity comprises a distance of 5cm or more between two points on the surface of the mold defining thecavity.
 11. The method of claim 1 wherein the mold cavity defines adistance of 10 cm or more between two points on the surface of the molddefining the cavity.
 12. The method of claim 5 wherein the mold cavitycomprises a distance of 2 cm or more between two points on the surfaceof the mold defining the cavity.
 13. The method of claim 6 wherein themold cavity defines a distance of 5 cm or more between two points on thesurface of the mold defining the cavity.
 14. The method of claim 7wherein the mold cavity comprises a distance of 5 cm or more between twopoints on the surface of the mold defining the cavity.
 15. The method ofclaim 7 wherein the mold cavity comprises a distance of 10 cm or morebetween two points on the surface of the mold defining the cavity. 16.The method of claim 8 wherein the mold cavity comprises a distance of 5cm or more between two points on the surface of the mold defining thecavity.
 17. The method of claim 8 wherein the mold cavity comprises adistance of 10 cm or more between two points on the surface of the molddefining the cavity.
 18. The method of claim 1 wherein the heating,mixing, collecting, defining, and dispensing are carried out using aninjection molding machine.
 19. The method of claim 1 wherein thepneumatogen source is an organic compound.
 20. The method of claim 1wherein the pneumatogen source is a pneumatogen.
 21. The method of claim1 wherein the pneumatogen is CO₂ or N₂.
 22. The method of claim 1wherein the dispensing comprises completely filling the mold cavity,further wherein the mold cavity comprises a volume of more than 1000 cm³and a distance of more than 2 cm between two points on the surface ofthe mold defining the cavity.